
GpigM°_ 



COPYRIGHT DEFOSiT. 



/ 

THE 



/0/0_ 

3 tri'o 



SCHOOL CHEMISTRY 

A NEW TEXT-BOOK 
FOR HIGH SCHOOLS AND ACADEMIES 



BY 
ELROY M. AVERY, Ph.D., LL.D. 

AUTHOR OF A SERIES OF TEXT-BOOKS ON PHYSICAL SCIENCE 



NEW YOHK-:. CINCINNATI • :« CHICAGO 

AMERICAN BOOK COMPANY 



Avery's Physical Science Series. 



FIRST LESSONS IN PHYSICAL SCIENCE. 

FOR USE IN GRAMMAR. SCHOOLS. 

(By Dr. Avery and Professor Sinnott.) 



ELEMENTARY PHYSICS. 
A SHORT COURSE FOR HIGH SCHOOLS. 



SCHOOL PHYSICS. 
FOR HIGH SCHOOLS AND ACADEMIES. 



SCHOOL CHEMISTRY. 
FOR HIGH SCHOOLS AND ACADEMIES. 



Copyright, 1904, by 
ELROY M. AVERY. 



Entered at Stationers' Hall, London. 



school chemistry. 
81 



Iln> Cooics *«*•»•"/«<» 

1904 

"5or,vr!pht Entry 
<JLATO oC XXc. No. 

930^7 

COPY B 



TO TEACHERS. 

If possible, have a well- ventilated room set apart for 
chemical operations. It is very desirable that this room 
l3e provided with a ventilating hood (see Appendix, § 23) 
connected with the chimney flue or the ventilating shaft. 
If you can not do this, keep an open fire burning, so that 
offensive gases and vapors may be removed from the room 
as well as possible in that manner. Provide working 
benches or tables, about 75 cm. (2f feet) wide. Each 
pupil should be allotted about a meter of working space 
at these tables, and held responsible for its condition. 

If the room is provided witli gas and water, a gas-cock 
and a water-cock, to which flexible tubing may be at- 
tached, should be within easy reach of each pupil. With 
pupils facing each other across a working bench of double 
width, it is possible to place the gas-cocks and the water- 
cocks so that one of each will accommodate four pupils. 
Over the benches place narrow shelves to hold the chemi- 
cal reagents ; beneath the benches place shelves or drawers 
for holding pieces of apparatus, etc. If the building is 
not connected with a regular water supply, see that water 
is always at hand in a tank or barrel, or in pails. A 
small cooking-stove will be a great convenience. 

If a room can not be set aside as a laboratory, flat tables 
may be laid upon the desks, and the reagents, apparatus, 
etc., kept in a cabinet or cupboard. Of course, a regu- 
larly fitted laboratory, with further and better means 
than those above suggested, is desirable, and should be 
provided when means can be secured for the purpose. 



4 TO TEACHERS. 

The chief significance of the foregoing is that, as far 
as possible, each pupil is to perform the experiments for 
himself, make his own observations, and draw his own 
conclusions. This is important, whether some of the 
experiments have been performed by the instructor before 
the class or not. In every case there must be care that 
the conclusions arrived at are founded upon actual facts. 

See that each pupil has a small note-book, and that he 
always has it at hand when he is making his experiments. 
See that the details of all experiments made by him are 
recorded by him in this book at the time of the experiment, 
not subsequently. In addition to the description of the 
operation, the record should contain an account of all 
observed phenomena, and the conclusions drawn from 
them. The ability to observe accurately and completely, 
and the ability to draw proper conclusions from observed 
facts, are the two greatest benefits to be derived from the 
study of general chemistry. 

Make frequent and careful examinations of the pupil's 
notes, seeking to lead him to accurate observation, to 
intelligent discrimination between essential and merely 
incidental conditions and results of an experiment, to 
correctness of conclusions, and to precision and concise- 
ness of statement. 

Do not let your pupils get the idea that they are 
chemists ; do not think that you ought to make chemists 
of them. After this course has been completed, a course 
in some good school of applied science will be needed for 
the pupil who desires to become a chemist. 

The author would be glad to receive suggestions from 
teachers using this book, or to answer any inquiries they 
may make. He may be addressed at Cleveland, Ohio. 
He gratefully acknowledges the aid given him by many. 
Especial mention is due to Professor Albert W. Smith of 
the Case School of Applied Science ; his work shows on 
almost every page. 



TO THE PUPIL. 

Have a place for everything and, when you are not 
using it, keep everything in that place. Clean every used 
utensil or piece of apparatus before you put it away T . 
Cleanliness is a necessity in the chemical laboratory. 
Habitually label every chemical that you put away or 
leave for a time. 

Before beginning an experiment, look over all your 
preparations, be sure that everything is ready and within 
easy reach, or you may suddenly discover a need for 
another hand. Be sure that all corks and connections 
are well fitted. Place your materials and apparatus at 
your left hand, and, when you have used them, lay them 
down at your right, keeping the middle of your bench 
clear for operating. 

Do not waste even inexpensive material. Be sure that 
you know why you do a thing before you do it. Always 
use the simplest form of apparatus. Do not think that 
you must have everything just as described by the author. 
If a Florence flask is called for by the text-book and you 
have not one, you may be able to get along with a bottle. 

Make careful notes on all experiments as they proceed. 
For this purpose, you should have a note-book with sub- 
stantial covers. Begin the account of each experiment 
with a brief statement of the object of the experiment; 
i.e., what you desire to prove or to illustrate by it. Then 
give a description of the process followed and of the 
apparatus used (a sketch is desirable), and record all 
observations. In conclusion, clearly state the inferences 
that you draw from what you have observed. Do not 
depend upon your memory to write up your notes after 

5 



b TO THE PUPIL. 

the experiment is finished. Some of your results thus 
recorded may subsequently be found to be incorrect. 
That is to be expected, and a repetition of the experiment 
will often be necessary. When you find that one of your 
results is wrong, mark it "Wrong," or "N.G." Do not 
be discouraged, but try to do better the next time. 

Ever keep in mind the fact that an experiment is 
intended to teach something, and that it can not serve its 
purpose unless it is accompanied by careful observation 
of the effects produced, and by equally careful study of 
the relations borne by these effects to the conditions 
of the experiment. 

Take an early opportunity for a careful reading of the 
Appendix to this book, so that you may be able to refer 
to it subsequently when you need help that it may give. 
The density (i.e., specific gravity) of all gases is referred 
to hydrogen as the standard. All temperatures are 
recorded in centigrade degrees. 



CONTENTS. 

CHAPTER PAGE 

I. The Domain of Chemistry 9 

II. Water and its Constituents: 

I. Analysis of Water 23 

II. Hydrogen 25 

III. Oxygen 34 

IV. Compounds of Hydrogen and Oxygen . . 47 

III. Air and its Constituents : 

I. Air 55 

II. Nitrogen .60 

JV. Some Nitrogen Compounds : 

I. Ammonia 64 

II. Nitrogen Oxides 70 

III. Nitrogen Acids, etc 77 

Y. Acids, Bases, and Salts 86 

VI. Valence, Rational Symbols, Radicals . . 93 

VII. The Halogen Group : 

I. Chlorine 97 

II. Hydrochloric Acid 105 

III. Other Chlorine Compounds . . . .112 

IV. Fluorine, Bromine, Iodine, and Manganese . 116 

VIII. Atomic and Molecular Weights, etc. . . . 127 

IX. Stoichiometry, etc 136 

X. Natural Groups — The Periodic Law . . . 143 

XL The First Group — Monads 149 

XII. The Second Group — Dyads: 

I. The Calcium Family 168 

II. The Zinc Family 178 

7 



8 CONTENTS. 

CHAPTER PAGE 

XIIL The Third Group— Triads : 

I. The Boron Family 187 

II. The Aluminum Family 191 

XIV. The Fourth Group — Tetrads: 

I. Carbon 106 

II. Carbon Oxides, etc. 205 

III. Relation of Carbon to Vegetable and Animal 

Life 216 

IV. Hydrocarbons in Homologous Series . . 219 
V. Illuminating-Gases 232 

VI. Some Derivatives of the Hydrocarbons . . 241 

VII. The Carbohydrates 265 

VIII. Other Elements of the Carbon Family . . 275 

IX. The Silicon Family 277 

XV. The Fifth Group — Pentads 289 

XVI. The Sixth Group — Hexads : 

I. The Chromium Family 314 

II. The Sulphur Family 317 

Note. — The Seventh Group was considered in Chapter VII. 

XVII. The Eighth Group: 

I. The Iron Family 348 

II. The Silver Family :)7:; 

III. The Platinum Family 380 

Appendix 390 

Index 413 



SCHOOL CHEMISTRY. 

CHAPTER I. 

THE DOMAIN OF CHEMISTRY. 

"Read Nature in the language of experiment." 

Experiment i. — Provide a small quantity of loaf sugar. Before 
going further be sure of your ability to recognize sugar by its appear- 
ance and its taste. If necessary to the development of such ability, 
use a magnifying glass for inspection, and dissolve some of the sugar 
in your mouth. Break the sugar lumps into small pieces, and experi- 
mentally determine whether the material that you are handling is 
still sugar. With mortar and pestle (see Appendix, § 12), pulverize 
the small pieces, and experimentally find out whether the powder is 
still sugar. In a beaker (see Appendix, § 8), dissolve 50 grams of 
this powder in 20 cubic centimeters (see Appendix, § 6) of hot water. 
When the liquid has cooled, set the beaker on a porcelain platter or 
a tin tray, add a little strong sulphuric acid to the syrup, and stir the 
two liquids together. The contents of the beaker will become hot, 
and, instead of the mixed liquids, we shall have a bulky, black, porous 
mass that has little resemblance to sugar or to sulphuric acid. In 
fact, the sugar has been changed to something that is not sugar; its 
identity has been destroyed. This experiment illustrates several 
fundamental facts that we shall now consider. 

1. Matter and Energy. — In the experiment above de- 
scribed we were dealing with things that occupied space 
and had weight. Anything that thus "takes up room" and 
has weight is matter. The different kinds of matter are 
called substances, as water, sugar, sulphuric acid, coal, 
silver, etc. That which brings about change in the posi- 
tion, condition, or nature of matter is called energy. One 



10 THE DOMAIN OF CHEMISTRY. 

agent that we call gravitation causes a body, i.e., a definite 
portion of matter, to fall to the earth ; gravitation is a form 
of energy. Another agent that we call heat causes ice to 
melt, and works many other changes ; heat is a form of 
energy. Another agent that we call chemism causes iron 
to rust and, in the above experiment, changed sugar into 
something that is not sugar. In the study that we are 
now beginning, we shall have much to do with this agent. 
Chemism is a form of energy. Energy is the general 
name for all the agents that effect such changes. In other 
words, energy is the power of doing ivork. 

Chemical Changes. 

Experiment 2. — With a pair of pincers, hold a piece of magnesium 
ribbon in a flame over a piece of black paper. The metal burns with 
a brilliant flame and loses its identity as magnesium. Instead of 
a metal, we have on the paper a white, brittle solid or powder. In 
this powder the most powerful microscope will reveal not the slight- 
est appearance of magnesium. Xot heat nor cold nor magnetism 
nor motion nor mechanical division of any kind will reproduce it. 
A chemical change has taken place, whereby the magnesium com- 
bined with oxygen derived from the air to produce magnesium oxide 
or magnesium rust. The process is similar to the rusting of any 
metal, except that it is extremely rapid. In this experiment, as in 
Experiment 1, another distinguishing characteristic of a chemical 
change may be observed. Heat was evolved. Every chemical change 
is accompanied by an evolution or an absorption of heat, or by its 
equivalent of electricity. 

Experiments. — Place about half a gram of tin-foil or turnings 
in a test-tube and cover it with about 10 cu. cm. of a mixture of 
equal parts of water and strong nitric acid. Care should be taken 
in handling this acid, as it is extremely corrosive. 1 Fold a strip of 

1 If such an acid comes into contact with the skin or clothing, the part 
affected should be promptly treated with dilute ammonia-water, and 
thoroughly rinsed with water. 




THE DOMAIN OF CHEMISTRY. 11 

paper two or three times upon itself and wrap it around the test- 
tube near its mouth to serve as a holder, or thus use a strip of asbes- 
tos paper. Gently warm the tube until all the metal has been changed, 
taking care not to breathe the gas evolved. Keep the acid nearly boil- 
ing for some time after the action is over, then allow the white solid 
to settle, carefully pour the acid into a 
porcelain dish, and evaporate it to dry- 
ness over a gas-flame. There will be 
little or no residue, showing that the 
tin has been converted into the white 
solid left in the tube. This is tin oxide 
or tin rust, and may be collected for 
further examination and preservation 
by washing it upon a filter-paper until 
it is free from acid. This is ascertained 
by testing the wash-water with blue 
litmus-paper, which is reddened by all 
acids. In this experiment the tin has 

entirely lost its identity, the white tin oxide possessing none of the 
characteristic properties of tin. There is no simply mechanical 
means by which the tin can be recovered. Hence we conclude that 
a chemical change has taken place. 

2. Changes in Matter. — From the foregoing experi- 
ments it appears that matter may be subjected to two 
kinds of change. In one of these, the substance does not 
lose its identity. In the other, the substance does lose 
its identity ; it becomes something else from which the 
original substance can not be recovered by purely mechani- 
cal means. Changes of this second kind usually involve 
an intimate contact of two or more substances, although 
sometimes only one is sensibly apparent. 

(a) Crushing, cutting, grinding, heating, cooling, magnetizing, and 
mixing with other substances are familiar examples of the first class 
of changes. The substance does not lose its identity, but may be 
restored, by merely mechanical means, to its first condition. Even 
when substances are melted or vaporized by heat, or are liquefied or 



12 THE DOMAIN OF CHEMISTRY. 

solidified by cold, they are restored to their original state and full 
identity when the original temperature is resumed. Changes of this 
kind are physical or mechanical changes. 

(6) When a metal rusts, when a body is charred or burned by acid 
or by fire, when an acid comes into contact with lime, soda, or any 
alkali, or in anyone of many other, cases, at least one substance is 
formed with properties different from those of the materials used. 
From this product, the original can not be recovered by mechanical 
means. The rust may be rubbed from the metal, but it is very 
different from the metal, and the compound formed by the acid and 
the soda is neither acid nor soda. Changes in which a substance thus 
loses its identity are called chemical changes. 

3. What is a Molecule? — If any body of matter is 
broken or cut in two, both parts are still of the same 
substance. As in Experiment 1, the dividing process may 
be many times repeated without changing the identity of 
the substance ; each bit of the sugar powder was as truly 
sugar as was the original lump. The question may arise 
whether such division without loss of identity can go on 
indefinitely. From the time of the great Greek philoso- 
phers this has been a disputed question. The prevailing 
chemical theory is that such a division can not go on 
indefinitely. Ultimately a portion is reached which, it 
is assumed, can not be again divided without destroying 
the identity of the substance. This particle, which is 
much smaller than the smallest that the best microscope 
can reveal, is called a molecule. 

(a) Heat is a kind of energy resulting from motion, but this 
motion is wholly invisible. The motion pertains to parts so minute 
and within limits so narrow that we can not detect the absence of any 
part from its original place. " A molecule may, therefore, be defined 
as a small mass of matter, the parts of which do not part company 
during the excursions which the molecule makes when the body to 
which it belongs is hot." 



THE DOMAIN OF CHEM1STKY. 13 

(A) The molecules of any given substance are held to be exactly 
alike, but different from the molecules of any other substance. For 
example, one copper molecule is exactly like every other copper mole- 
cule, but different from every molecule of any substance that is not 
copper. The nature of the substance, therefore, depends upon the 
nature of its molecule. See § 4 (a). 

(c) Any change, then, that does not affect the composition of the 
molecule is a physical change, because it produces no change in the 
identity of the substance; any change that does affect the composition 
of the molecule is a chemical change. 

((/) Division of the molecule implies the existence of a smaller por- 
tion of matter than a molecule. These smaller particles into which 
molecules are divided by chemical changes have been given a special 
name. 

4. What is an Atom ? — The constituent parts of a mole- 
cule are called atoms. Nearly every molecule consists of 
two or more atoms ; some molecules are very complex. 
As we shall see, the water molecule consists of two atoms 
of hydrogen and one of oxygen (H 2 0); the sugar mole- 
cule consists of twelve carbon atoms, twenty-two hydro- 
gen atoms, and eleven oxygen atoms, — forty-five in all 
(C 12 H 22 O n ). In Experiment 1, the sulphuric acid broke 
up the sugar molecule by abstracting its hydrogen and 
oxygen atoms and leaving carbon atoms that made up the 
residual charcoal. According to the generally accepted 
theory, an atom is one of the component parts of a molecule, 
and is indivisible by chemical means. 

(«) In the preceding paragraph it is stated that the nature of the 
molecule determines the nature of the substance. Tt should be under- 
stood that the nature of the molecule is affected not only by the kind 
and the number of its constituent atoms, but also by the way in which 
those atoms are grouped or linked to form the molecule. 

5. Elementary and Compound Substances. — Any sub- 
stance that can not be separated, by any knoicn means, into 



14 THE DOMAIN OF CHEMISTRY. 

two or more essentially different kinds of matter, is called an 
element. Any substance that can be thus separated is called 
a compound. Compounds consist of two or more elements 
in chemical combination. The atoms of any given element 
are of the same kind; those of a compound are of two or 
more kinds. There are as many kinds of atoms as there are 
elements. Nearly four score elements have been already 
recognized (see Appendix, § 1). Some of these are very 
abundant and widely distributed ; others have been found 
only in such minute quantities that their properties have 
not been satisfactorily determined. Other elements will 
doubtless be discovered, and it is possible that some sub- 
stances now considered elementary will be found to be 
compound. In fact, nearly every improvement in our 
methods of examination leads to the detection of elements 
previously unknown. Silver and gold are elements ; wood 
and water are compounds. 

(a) The elements are sometimes classified as metals and non-metals, 
but the classification has lost much of its earlier importance. Iron, 
copper, gold, and silver are metals, and the properties familiarly asso- 
ciated with them are sufficiently definitive of the word metal as it 
will be used in this book. Of the groups into which compounds are 
divided, the most important three are acids, bases, and salts. These 
groups will be considered in a later chapter. 

6. Atomic Attraction. — The attraction existing between 
atoms pertains chiefly to chemistry. Atomic attraction is 
called chemism or chemical energy. 

Chemical Energy. 

Experiment 4. — Pulverize separately a teaspoonful each of loaf 
sugar and potassium chlorate (chlorate of potash) and mix them to- 
gether upon a porcelain plate. Dip a glass rod (see Appendix, § 5, a) 



THE DOMAIN OF CHEMISTRY. 15 

into strong sulphuric acid and hold the rod in a horizontal position 
over the mixture and close to it but so as not to touch it. Notice that 
there is no peculiar action visible. Now hold the rod in a vertical 
position, so that a drop of acid will fall upon the mixture. The mix- 
ture is immediately ignited. 

Experiment 5. — Into a mortar, put a bit of potassium chlorate not 
larger than a grain of wheat, and cover it with powdered sulphur. 
Notice that there is no peculiar action visible. Now rub them 
together vigorously with the pestle. A sharp explosion or a suc- 
cession of minute explosions will take place. 

Caution. — Phosphorus should not be handled with naked, dry 
fingers. It ignites easily by friction or slight elevation of temperature. 
Phosphorus burns are serious. Under water, it may be handled and 
even cut with safety. When taken directly in the fingers, the fingers 
should be wet. " Better be careful than sorry." 

Experiment 6. — Cover a bit of phosphorus, the size of a pin-head, 
with pulverized potassium chlorate and wrap the materials in a bit of 
soft paper, so as to form a minute torpedo. The phosphorus and the 
particles of potassium chlorate lie close together, but no action takes 
place. Now place the torpedo on a small anvil or other smooth, hard 
surface and force the phosphorus and potassium chlorate closer 
together by a blow with a hammer. A violent explosion takes place. 

7. Limitation of Chemical Energy. — The foregoing ex- 
periments illustrate the fact that atomic attraction is effec- 
tive at insensible distances only. In only a few cases is it 
possible by mechanical means to bring solid particles suf- 
ficiently near each other for the desired chemical action. 
The necessary freedom of molecular motion is generally 
secured by solution, fusion, or vaporization of one or more 
of the materials used. Hence solvents and heat are im- 
portant agents in the chemical laboratory. 

(a) A body is dissolved or " in solution " when it is so finely divided 
and its particles are so completely dispersed through the water or other 
solvent that they can neither be seen nor separated from the liquid by 
filtering. 



16 THE DOMAIN OF CHEMISTBY. 

Chemical Action. 

Experiment 7. — Rub together in a mortar 4 grams of sodium sul- 
phate crystals and 2 grams of potassium carbonate. The two solids 
form a liquid. Repeat the experiment with ice and salt. 

Experiment 8. — Saturate 4 cu. cm. of water with calcium chloride. 
Add slowly 0.5 cu. cm. of sulphuric acid. The two transparent liquids 
form a white, opaque solid. 

Experiment 9. — Moisten the inner surface of a beaker, or of a clear 
tumbler, with strong ammonia-water, and place a few drops of the 

liquid in the glass. Cover 
it with a glass plate (or a 
piece of writing paper). 
Moisten the inner surface 
of a similar clear glass 
vessel with hydrochloric 
(muriatic) acid. Invert 
the second vessel over the 
first, mouth to mouth, so 
that the contents of the 
two vessels shall be sep- 
arated only by the plate. 
FlG - % Each vessel is filled with 

an invisible gas. Now remove the plate. The invisible gases diffuse 
into each other and form a dense cloud that slowly settles in the form 
of a white powder. 

Experiment 10. — In a conical test-glass, or in a test-tube, dissolve a 
few crystals (0.5 of a gram) of silver nitrate in 10 cu. cm. of water. 
In a second test-glass, place a similar solution of lead nitrate ; in a 
third, a solution of mercuric chloride (corrosive sublimate) ; in a 
fourth, 10 cu. cm. of chlorine-water (see Experiment 88), to which 
a few drops of a freshly prepared dilute solution of starch have been 
added. Each solution will be as clear as water. To each, add a few 
drops of the colorless solution of potassium iodide, and notice the 
colors produced, yellow, orange, Bcarlet, and blue. 

Experiment n. — Into a glass tube 2 cm. in diameter, and 15 or 
20 cm. in length, having one end closed and rounded like a test-tube, 
place 20 milligrams of freshly burned charcoal. Draw the upper part 





THE DOMAIN OF CHEMISTRY. 17 

of the tube out to a narrow neck. Fill the tube with dry oxygen and 
seal the tube by fusing the neck. Weigh the tube and its contents 
very carefully. By gradually heating 
the rounded end of the tube, the char- 
coal may be ignited and, with sufficient 
Gare, entirely burned without breaking 
the tube. When the charcoal has dis- 
appeared, weigh the tube and its con- 
tents again. The chemical changes that 
led to the disappearance of the charcoal 
have caused no change in the weight of 
the materials used (see Appendix, § 5, 
c and d). *■*" fig. 3. 

8. Conservation of Mass and Energy. — From the pre- 
ceding paragraphs we learn that atomic attraction is a 
very powerful agent, but that it acts only upon the minut- 
est divisions of matter and at distances too small to be 
perceptible. The resulting action leads to a change of 
identity and to a general change of properties excepting 
weight. This exception is the direct result of the inde- 
structibility of matter. Every atom of matter has a cer- 
tain definite weight, and as, in these changes, the atoms 
are merely rearranged, the sum total of the weights of 
these atoms must remain unchanged. This is called the 
law of the persistence or of the conservation of mass. As 
will be seen from the next paragraph, chemical action 
takes place between definite quantities of matter only. 
The law of the conservation of mass finds a parallel in 
the law of the conservation of energy, — one of the most 
important generalizations of modern science. The vari- 
ous kinds of energy may be transformed from one to 
another, but the total energy is not thereby increased or 
diminished. 

SCHOOL CHEMISTRY 2 



18 



THE DOMAIN OF CHEMISTRY. 



Constituents Free or Combined. 

Experiment 12. — Fine iron-filings and powdered sulphur may be 
mixed in any proportion. From such a mixture the iron may be 
removed by a magnet ; the sulphur may be removed by solution in 
carbon disulphide, nitration, and subsequent evaporation of the fil- 
trate. The iron is still iron, the sulphur is 
still sulphur. In the mixture the free iron 
or sulphur particles may be detected with a 
microscope. Now mix thoroughly 4 grams of 
the powdered sulphur with 7 grams of the 
iron-filings, and place the mixture in an igni- 
tion-tube (see Appendix, § 5, a) about 12 cm. 
long. By wooden nippers, hold the tube over 
the gas- or the alcohol-lamp, as shown in the 
figure. Part of the mixture may be similarly 
heated in the bowl of a common clay pipe 
instead of the ignition-tube. The sulphur 
melts and combines with the iron to form a 
sulphide of iron. There is no longer anything 
to be attracted by a magnet, or to be dissolved 
The microscope reveals no particle of either 
constituent of the mixture. The ferrous sulphide, which contains the 
iron and the sulphur, differs from both in appearance and properties. 
It always consists of 7 parts of iron to 4 parts of sulphur by weight 
(or 56 : 32) , however or wherever obtained. 




by carbon disulphide. 



9. Mixtures and Compounds. — Mixtures of two or 
more substances may be formed by mingling them in 
all conceivable proportions, but a compound formed by 
chemical action consists of certain invariable proportions 
of its constituents. Thus, oxygen and hydrogen may be 
mixed in any desired proportion, but they will unite to 
form water only in the ratio of eight parts to one by 
weight, or one part to two by volume. In a mixture, the 
constituents are said to be free ; in a compound, they are 
said to be combined or in combination. 



THE DOMAIN OF CHEMISTRY. 19 

(a) Gunpowder is composed of charcoal, sulphur, and potassium 
nitrate (niter or saltpeter) mechanically mixed. The potassium 
nitrate may be washed out by water, and, by evaporating the water, 
may be secured in the solid form. The sulphur may then be removed 
from the mixture, as in Experiment 12. The charcoal will be left 
alone. The constituents of gunpowder could not be thus separated 
if they were in chemical union. "When gunpowder is ignited, the 
constituents combine to form enormous volumes of gaseous products. 

10. Chemistry Defined. — Chemistry is the branch of phys- 
ical science that deals with changes in the identity of substances, 
and, hence, with all changes ivithin the molecule. It treats 
of the laws, causes, and effects of elemental combination. 

11. Atomic Symbols. — Chemists have a short-hand 
way of writing the names of the substances with which 
they deal. In chemical notation, each element is repre- 
sented by the initial letter of its Latin name. When the 
names of two or more elements begin with the same letter, 
the initial letter is followed by the first distinctive letter 
of the name. Thus, C stands for carbon, Ca for calcium, 
and CI for chlorine. This use of the initial letters of Latin 
names secures uniformity among chemists of all countries. 
In only a few cases do the Latin and the English initials 
differ. The symbols of all the elements may be found in 
the list on the third page of the cover of this book. These 
symbols are frequently used to represent their respective 
substances in general. Thus, for the sake of brevity, we 
may write " a liter of O," but in the symbols (i.e., for- 
mulas) of compound bodies, and in equations represent- 
ing chemical reactions (§ 141), the symbol of an element 
represents a single atom. To represent several atoms, we 
use figures placed at the right of the symbol and a little 
below it. Thus, C 2 means two atoms of carbon. 



20 THE DOMAIN OF CHEMISTRY. 

12. Molecular Formulas. — The symbol of a molecule is 
formed by writing together the symbols of its constituent 
atoms, indicating the number of each kind, as just stated. 
A molecule of water consists of three atoms, two of hydro- 
gen and one of oxygen ; hence, its symbol is H 2 0./ Like 
the atomic symbols of the elements, these s} T mbols' of the 
molecules of compound substances are used to represent 
their respective substances. Thus, we sometimes speak 
of a. liter of H 2 0, but in the equations representing re- 
actions, each of these symbols represents a single molecule. 
To represent several molecules, we place the proper figure 
before the symbol. Thus, 3H 2 represents three mole- 
cules of water. The symbol of a molecule is often called 
its formula. Chemical notation is the written language 
of the science. 

13. Nomenclature of the Elements. — The nomenclature 
of chemistry is the result of an attempt to indicate the 
composition of a substance by its name. The names of 
the elements were generally chosen arbitrarily, although 
some of them allude to some prominent property, as chlo- 
rine from the Greek chloros, signifying green. Chemical 
nomenclature is the spoken language of the science. 

14. Nomenclature of Binary Compounds. — The names 
of binary compounds (those containing only two ele- 
ments) have the characteristic termination -id or -ide. 
Compounds of single elements with oxygen are called 
oxides, similar compounds with chlorine are called chlo- 
rides, those with sulphur are called sulphides, etc. Thus, 
we have lead oxide, silver chloride, and hydrogen sul- 
phide. When any two elements unite in more than one 



THE DOMAIN OF CHEMISTRY. 21 

proportion, one or both of the words constituting the 
name are modified, as in hydrogen peroxide, carbon disul- 
phide, mercurous chloride, and mercuric chloride. 

Xote. — In an attempt to simplify the spelling of chemical names, 
many chemists write chlorin, instead of chlorine ; chlorid instead of 
chloride ; oxid, snlphid, etc. It is not yet apparent whether the 
attempt is to end in success or failure. In either event, no ambiguity 
will annoy the student of this book. 

15. Nomenclature of Ternary Compounds. — The most 
important compounds containing three or more elements 
are the acids (see § 89). Most of these consist of hydro- 
gen and oxygen united to a third, or characteristic, ele- 
ment that gives its name to the acid. The terminations 
-ic and -ous are used with the name of the characteristic 
element to indicate a greater or less amount of oxygen in 
the acid. Thus we have : 

Nitric acid HX0 3 I Sulphuric acid .... H 2 S0 4 

Nitrous acid HX0 2 | Sulphurous acid . . . H 2 S0 3 

At least a part of the hydrogen of an acid may be 
replaced with different metallic elements, giving us the 
large and important class of compounds called salts (see 
§ 91). The generic name of the salt is formed by chang- 
ing the -ic termination of the name of the acid to -ate, or 
by similarly changing -ous to -ite. Thus, phosphoric? acid 
furnishes phosphates, while phosphorus acid furnishes 
phosphites. The specific name of the salt is derived from 
that of the element used to replace the hydrogen of the 
acid . Thus we have : 



Nitric acid HX0 3 

Nitrous acid HX0 2 

Sulphuric acid .... H 2 S0 4 

Sulphurous acid . . . H 2 S0 3 



Potassium nitrote . . . KX0 3 

Potassium nitrite . . . KX0 2 

Potassium sulphate . . K 2 S0 4 

Potassium sulphite . . K 2 S0 3 



22 THE DOMAIN OF CHEMISTRY. 

(«) Some chemists prefer to modify the name of the replacing ele- 
ment, making it an adjective, e.g., potassic nitrate. In the case of 
English words that can not be adapted to - such ail/eotive forms, the 
Latin word is used ; e.g., plumbic nitrate for lead nitrate. In some 
cases old forms are still frequently used ; e.g., chlorate of potash for 
potassium chlorate. In some cases, a strict adherence to systematic 
chemical nomenclature would lead to the use of inconvenient names, 
as potassium-aluminum sulphate for common alum. 



CHAPTER II. 
WATER AND ITS CONSTITUENTS. 

I. ANALYSIS OF WATER. 

Experiment 13. — The apparatus represented in Fig. 5 consists of a 
vessel containing water (to which a little acid has been added to in- 
crease its conductivity) in which are immersed two platinum strips, 
the electrodes of a galvanic battery. Glass tubes containing acidulated 




water are inverted over the platinum electrodes. A battery of one or 
two good storage cells or of three or four Grove cells will answer very 
well for our present purpose. When the circuit is closed, bubbles will 
be noticed rising in the glass tubes and gradually displacing the water 
therefrom. Gas will accumulate about twice as rapidly in one tube 
as in the other. 

16. The First Question. — One of the most familiar sub- 
stances in nature is water. Perhaps we do not know of 
23 



24 



WATER AND ITS CONSTITUENTS. 



what it is made, or whether it is an element or a compound. 
By the time the water has been displaced from one of the 
tubes, Ave shall, perhaps, be wondering what is in the tube. 
This question, " What is it ? " is continually recurring to 
the chemist. Lift the tube carefully, holding it mouth 
downward, and cover its mouth with the thumb. It looks 



like air ; is it air \ 




To obtain our answer, we must, as 
usual, make an experiment. 

Experiment 14. — Light a taper or a dry 
splinter of wood, and thrust it into the 
tube. The taper-flame will be extinguished 
and the gas will burn at the mouth of the 
tube. Notice the appearance of the flame. 
The taper may be withdrawn and relighted 
at the mouth of the tube and the experi- 
ment repeated. We have received the 
answer to our experimental inquiry. It is 
not air. It is a gas lighter than air and 
inflammable. It has been named hydrogen. 



17. What is in the other tube ? — By this time the 
other tube is probably full of gas. If so, break the elec- 
tric circuit and remove the tube, closing its mouth as 
before. Is it air ? Is it hydrogen ? 

Experiment 15. — To put these questions in proper form, light the 
taper and let it burn until a spark will remain upon the wick when 
the flame is blown out. Thrust the glowing taper (or a glowing 
splinter) into the tube. The taper is rekindled and burns with un- 
usual vigor and brilliancy. The answer is as prompt and unmistakable 
as before. It is not air; it is not hydrogen. It is a gas that supports 
combustion much more vigorously than air does. It is called oxygen. 

18. Analysis and Synthesis. — By chemical analysis, we 
mean the breaking up of a compound into its constituent 
parts (see Experiment 29) ; by chemical synthesis, we mean 



ANALYSIS OF WATER. 25 

the union of two or more substances to form one, different 
from any of its constituents (see Experiment 39). Syn- 
thesis may be used to prove the results of analysis. 

19. The Synthesis of Water. — So far, we have seen 
that water is composed of oxygen and hydrogen, there 
being twice as great a volume of the latter as of the for- 
mer. If we desire to know whether water has any other 
constituent, or suspect that these gases came from the 
small quantity of acid used to increase the electric con- 
ductivity of the water, it would be natural to try to unite 
these gases and to see what the product is. For such an 
experiment we are not quite ready. By the analysis of 
something we have secured separated oxygen and hydro- 
gen ; for their synthesis, it is desirable that we know 
more about them. 

II. HYDROGEN. 
Symbol, H ; density, 1 ; atomic weight, 1 ; valence, 1. 

20. Occurrence. — Free hydrogen occurs in nature as a 
small constituent of natural gas, of some volcanic gases, 
and of the gases of some coal mines. It is known to 
exist in some meteorites, in the nebula?, and in other stellar 
bodies. It is a small but constant constituent of our 
atmosphere. In combination, it is almost everywhere, 
being found in water, in petroleum, and in all animal and 
vegetable substances. > 

21. The Apparatus. — Provide a good bottle, about 
twenty centimeters (8 in.) high, and having a mouth about 
two and five-tenths centimeters (1 in.) in diameter. See 
that the edges of the bottle are smooth. To the mouth of 



26 



WATER AND ITS CONSTITUENTS. 



this bottle fit a fine-grained cork or a rubber stopper pierced 
with two holes. Furnish it with a funnel-tube, a, and a 
delivery-tube, b (see Appendix, § 5, 5). The funnel-tube 
should be of such a length that, when the cork is in its place, 
the tube will reach within one centimeter (^ in.) of the 
bottom of the bottle. In all cases the sharp edges of glass 
tubing should be rounded in the gas-flame, to prevent its 
cutting the stopper or the rubber tubing and thus causing 
the apparatus to leak. To the delivery-tube, 6, connect a 




piece of glass tubing, d, bent near each end. The 
connection may be made by a short piece of snugly 
fitting rubber tubing, c. If desirable, c and d may be 
replaced by a piece of rubber tubing of suitable length. 
The lower end of d terminates beneath the inverted 
saucer or tin plate, e, placed in the pan, /. The saucer 
has a notch in its edge for the admission of £?, and a hole 
in the middle of its bottom; this hole should be a little 
larger than the delivery-tube. Into the pan, pour enough 
water to cover the saucer. Fill a bottle, g, with water and 
invert it over the hole in the bottom of e. Atmospheric 
pressure will keep the water in g. 



HYDROGEN. 27 

22. The Preparation. — Melt about 125 grams (4 oz.) of 
zinc in a clay crucible or an iron ladle, and slowly pour 
it, while very hot, into a pail or a tub of water, from a height 
of several feet. Put twenty-live or thirty grams (1 oz.) of 
this granulated zinc or of clippings of ordinary sheet zinc 
into the gas-bottle, B, pour in water until the bottle is 
about a quarter full, and replace the cork. Be sure that 
all of the joints about the mouth of the bottle are tight. To 
test this, place the delivery-tube between the lips and 
force air into the bottle until water rises in the funnel-tube 
and nearly fills it. Place the end of the tongue against 
the end of the delivery-tube to prevent the escape of air 
from the bottle. If the water retains its elevation in a, 
the joints are tight. If the water falls in a to the level 
of that in B, the apparatus leaks and must be put into 
satisfactory condition before going on. Pour dilute sul- 
phuric or hydrochloric acid through the funnel-tube, a, 
in small quantities, not more than a thimbleful at a time. 
Gas will be generated with lively effervescence in B and 
bubble up in g, displacing the water therefrom. This 
method of collecting a gas, by the displacement of water, 
is called "collecting over water." 

23. The Collection. — The gas first delivered will be 
mixed with the air that was in the apparatus at the be- 
ginning of the experiment. This should be thrown away, 
as it is dangerously explosive. When a quantity of gas 
about equal to the contents of the gas-bottle has thus been 
allowed to escape, fill a test-tube or a small wide-mouthed 
bottle with the gas, remove it from the water-pan, being 
careful to hold it mouth downward, and bring a lighted 



28 WATER AND ITS CONSTITUENTS. 

match or other flame to the mouth. If the gas burns 
with a puff, or a slight explosion, it is not yet free from 
air. In this way continue to test the gas until a sample 
burns quietly at the mouth of the tube and within it. 
Keep the end of the delivery-tube, cZ, under water until 
you are sure that the hydrogen is unmixed with air. 
Do not, at any time, bring a flame into contact with any con- 
siderable quantit}^ of hydrogen until you have established 
its non-explosive character by testing a small quantity as 
just described. For such tests, bottles are not so good as 
test-tubes or cylinders as they confine the gas more and 
thus increase the danger in case of an explosion. Add 
acid through the funnel-tube from time to time, as may be 
necessary to keep up a brisk effervescence in the gas-bottle. 
Fill several bottles with the unmixed gas, slipping the 
mouth of each, as it is filled, into a saucer containing 
enough water to seal the mouth of the bottle and thus to 
prevent the escape of the hydrogen. If you have used the 
pneumatic trough (see Appendix, § 13) instead of the water- 
pan, the bottles may be left upon the shelf of the trough, 
which should be a little below the surface of the water. 
At your earliest convenience, fill one of the gas-holders (see 
Appendix, § 14) with hydrogen. At the end of the experi- 
ment, pour off some of the clear liquid from the gas-bottle, 
and evaporate it in a porcelain dish over a lamp until a solid 
begins to separate. Then allow the liquid to cool and 
examine the crystals that form. 

24. The Reaction. — The hydrogen just prepared resulted 
from the action of the zinc upon the acid, water being used 
to dissolve the solid compound thus formed. Resulting 



HYDROGEN. 29 

from this action we have the hydrogen gas and a chemical 
compound called zinc chloride if hydrochloric acid was 
used, or zinc sulphate if sulphuric acid was used. This 
compound remains dissolved in the water of the gas-bottle. 
The zinc chloride or sulphate is obtained by evaporating 
the solution. Hydrochloric acid is composed of hydrogen 
and chlorine ; its molecular formula is HC1. The zinc 
chloride is composed of zinc and chlorine and is represented 
by ZnCl 2 . The changes that took place in the bottle may 
be represented by the following equation (see § 141) : 

Zn + 2HC1 = ZnCl 2 + H 2 + heat. 

The free zinc united with the chlorine of the acid to 
form the zinc chloride, thus setting free the hydrogen of 
the acid. As hydrogen is a gas, it bubbled through the 
water causing the effervescence. As zinc chloride is a 
soluble solid, it was dissolved by the water. From the 
clashing together of atoms in this reaction, much heat was 
developed. At the close of the experiment, small black 
particles are sometimes to be seen floating in the solution 
in the gas-bottle. These are bits of carbon that were 
present, as impurities, in the zinc. 

■ Physical Properties of Hydrogen. 

Experiment 16. — Instead of " collecting over water," collect the gas 
by "upward displacement," as follows: Bring the delivery- 
tube, d, of the gas-bottle (Fig. 7) or of the gas-holder into 
a vertical position. Holdover it a test-tube, or a small bottle, 
and cause the hydrogen to flow rapidly through the tube,d. 
In a few moments the air will be driven from the test-tube 
and replaced with hydrogen. That this gas is not mixed 
with air (after allowing the hydrogen to flow a sufficient ^ 
length of time) may be shown by testing it in the manner 
described in § 23. What does this experiment teach? 




30 



WATER AND ITS CONSTITUENTS. 




Experiment 17. — Refill the bottle with hydrogen, cover the mouth, 
turn the bottle right side up, remove the cover, and quickly apply a 
flame. How does the hydrogen flame differ from those previously 
seen? Why? 

Experiment 18. — Take two cylinders or large test-tubes of equal 
size. Fill one of them, a, with hydrogen. 
Bring the mouth of a to that of b, gradually 
turn a from its inverted position, until it is 
upright below b. Place a upon a table and, 
in half a minute, test the two tubes with a 
flame. If the experiment has been neatly 
performed, it will be found that the hydro- 
gen was poured upward from a to b. This 
" iqrvvard decantation " is possible because 
of the extreme levity of this gas as compared with the surrounding air. 
Experiment 19. — Equipoise two beakers. Fill the inverted beaker 
with hydrogen by 
upward decantation. 
The equilibrium will 
be destroyed, and the 
glass containing hy- 
drogen will rise. 

Experiment 20. — 
To the flexible rubber 
delivery-tube of a gas- 
holder containing hy- 
drogen, attach the 
stem of an ordinary 
clay pipe, or of a small 
glass funnel. With 
the gas flowing slowly 
(the flow being con- 
trolled by the stop- 
cock), dip the pipe 
into a dish of soap- 
suds, and, when a film 
is formed over the mouth of the pipe, turn its mouth upward and 
open the stop-cock wider. The bubble will soon break away from 
the pipe and rise like a balloon. 




HYDROGEN. 



31 



Xote. — The last experiment will be more satisfactory if the soap- 
suds is prepared by making a strong solution of white castile soap in 
warm soft water that has been recently boiled, and adding half its 
volume of glycerin. Shake the mixture thoroughly, and it is ready 
for use. 

Experiment 21. — Over a vertical tube delivering hydrogen, hold a 
sheet of gold-leaf or of unglazed paper. The gas will pass through 
the gold or the paper, and may be lighted on the upper side of the 
sheet. 

Experiment 22. — The remarkably rapid diffusion of hydrogen may 
be shown by closing one end of a glass tube 3 or 4 cm. in diameter and 
about 30 cm. long, with a plug of plaster of Paris 1 or 2 cm. thick, fill- 
ing it with hydrogen by upward displacement and placing the mouth 
of the tube in a tumbler of water. The outw T ard diffusion of the gas 
through the porous septum reduces the pressure on the water in the 
tube, which is then forced upward by atmospheric pressure. An 
. argand lamp chimney answers w r ell for the experiment. The plug- 
may be inserted by spreading a stiff paste of the plaster and water in a 
layer of the desired thickness upon a piece of writing-paper and press- 
ing one end of the chimney down into it. In an hour or two the plaster 
will have set. The paper may then be easily 
removed and the plaster outside the tube 
broken off. Allow it to dry over night 
before using. In filling the tube with gas, 
hold it so that the septum will be covered 
with the fleshy part of the hand to prevent 
premature diffusion. The water may be 
colored with cochineal or indigo or ink. 

Experiment 23. — To show the effect of 
hydrogen upon sounds produced in it, fill a 
large bell-glass with the gas, suspend it 
mouth downward, and strike a bell in it. 
Instead of the bell, one of the small squeak- 
ing toys well known to children may be 
sounded in the hydrogen. 




25. Physical Properties. — Hydrogen is a transparent, 
colorless, tasteless, odorless gas, as may be seen by direct 



32 



WATER AND ITS CONSTITUENTS. 



inspection. Excepting possibly ethereon, 1 it is the lightest 
known substance. One liter of it weighs almost exactly 
0.09 grams. It has been liquefied and solidified by subject- 
ing it to a very great pressure at a very low temperature. 
Liquid hydrogen boils (i.e., changes to a gas) at — 240°, 
and is one of the lightest liquids, its density being only 
0.07. Because of its extreme lightness, the gas diffuses 
very rapidly and has a peculiar effect upon sounds pro- 
duced in it. It is only sparingly soluble in water. 

(«) Hydrogen is about 14i times as light as air, and about 11,000 
times as light as water. 

(b) That hydrogen is not very soluble in water is shown by the 
fact that it may be collected over water. But the metal palladium 
absorbs or "occludes" several hundred times its volume of hydrogen, 
forming what seems to be an alloy. For this reason, and because of 
its chemical properties, hydrogen may be considered the vapor of a 
highly volatile metal. 

Chemical Properties of Hydrogen. 

Experiment 24. — Repeat Experiment 14, and describe 
the phenomena fully. What two chemical properties 
of hydrogen does this experiment 
illustrate ? 

Experiment 25. — Repeat Experi- 
ment 20, and, while the bubble is in 
the air, touch it quickly with a lighted 
taper. Be sure to see all that the 
experiment shows, and then tell what 
you see. 

Experiment 26. — For the bent 

delivery-tube of the gas-bottle, substi- p 
tute a straight one having the upper ^=3 
part drawn out to form a jet. After Fig. 13. 

1 Certain physical facts point to the existence of an element at least a 
thousand times as light as hydrogen. It has been provisionally named 
" ethereon," but its existence has not yet been definitely proved. 





HYDROGEN. 



33 



the hydrogen has been escaping for some time, test small quantities 
of it until you are sure that it is unmixed with air. Then wrap 
a towel several times around the bottle (as an added precaution) 
and apply flame to the jet. Hold a small coil of fine wire in the 
upper part of the flame. Describe fully the flame of this " Philosopher's 
candle." 

Experiment 27. — Over the flame of the "Philosopher's candle" 
hold a clear, dry, cold tumbler. In a few moments the clear glass 
will become dimmed with a sort of dew, evidently caused by the con- 
densation of some vapor formed by the burning of hydrogen in air. 

Experiment 28. — Pass hydrogen through a tube filled with granu- 
lar calcium chloride to remove all moisture, and then through a tube 
terminating in a jet. After tests have shown that unmixed hydrogen 




is passing, ignite the gas at the jet. Over the jet place a bell-glass 
that is kept cool by a cloth wet with cold water. A liquid will collect 
on the inner surface of the cold glass ; after a time it may be made to 
run into a cup below. This liquid may be shown to be pure water. 



26. Chemical Properties. — Hydrogen is combustible at 
about 500°, i.e., it combines chemically with the oxygen 
of the air at that temperature. Its flame is pale but 



SCHOOL CHEMISTRY 3 



34 WATER AND ITS CONSTITUENTS. 

intensely hot. The burning of one gram of hydrogen 
yields more than 34,000 calories, it having the greatest 
heating power of any known substance. Whenever 
burned, either in the free state or in combination with 
other elements (e.g., alcohol or petroleum), the product 
of its combustion is water. It does not support ordi- 
nary combustion or respiration. When immersed in it, a 
lighted taper is extinguished and an animal is suffocated, 
in both cases because of the absence of oxygen. It forms 
an explosive mixture with air or oxygen. 

Note. — In the periodic system of the chemical elements (§ 148, b), 
hydrogen falls in Group 1, the other members of which are considered 
in Chapter XI. 

27. Uses. — On account of its lightness, hydrogen has 
been used for the inflation of balloons. On account of 
the intense heat produced by its combustion, it is used 
for melting platinum and other refractory substances, 
and in producing the calcium light (see Experiment 46). 
It is useful in reducing metallic oxides, the metals thus 
formed being remarkably free from impurities. 

28. Tests. — Hydrogen is easily identified by its physi- 
cal properties, especially its lightness, its ready inflamma- 
bility, and the extinction of a flame placed in it. 

III. OXYGEN. 
Symbol, O ; density, 16 ; atomic weight, 10 ; valence, 2. 

29. Occurrence. — Of all the elements, oxygen is the 
most abundant and the most widely diffused. One-fifth 
of the air, by weight, is free oxygen, and eight -ninths of 



OXYGEN. 35 

water, by weight, is combined oxygen. It has been esti- 
mated that fully two-thirds of the accessible world is 

oxygen. 

Preparation of Oxygen. 

Experiment 29. — Place about 10 grams of mercuric oxide in an 
ignition-tube, fit it with a perforated cork carrying a delivery-tube, 
and support it in any convenient way. Heat it gently with a gas- or a 
lamp-flame, and collect the evolved gas in bottles over water. When 
no more gas comes over, remove the delivery-tube from the water and 
then remove the lamp. When the ignition -tube has cooled, examine 
the material left on its walls. A molecule of mercuric oxide (HgO) 




is composed of one atom of mercury and one of oxygen. When heat 
is applied, these atoms separate from each other and reunite with 
atoms of their own kind to produce metallic mercury and oxygen gas. 
Compare the metal thus obtained with some from the laboratory col- 
lection and see if they are alike. Also see that the gas has the proper- 
ties of one of those obtained in Experiment 13. 

Caution. — Commercial manganese dioxide is sometimes adulter- 
ated with carbon. When such a mixture is heated with potassium 
chlorate, it gives rise to dangerous explosions. Hence, a new or 
doubtful sample may well be tested on a small scale by heating it with 
potassium chlorate in a test-tube. 

Experiment 30. — Pulverize five grains of clean potassium chlorate 
(KC10 ;j ) and mix it thoroughly with an equal weight of black oxide 
of manganese (manganese dioxide, Mn0 2 ) that has been previously 



36 



WATER AND ITS CONSTITUENTS. 



heated to redness and allowed to cool. Place the mixture in an igni- 
tion-tube, or a piece of gas-pipe, of such size that the tube will be not 
more than a third full. Keep the mixture four or five inches from 
the ends of the tube by plugs of asbestos or of glass wool. Close the 
ends of the tube with corks, one of which carries a delivery-tube. 
Support the ignition-tube in a slanting position and apply heat. The 
part of the mixture near the delivery-tube should be heated first and 




the heat so regulated that the evolution of gas is nearly uniform. 
Collect the gas over water in bottles of about 250 cu. cm. capacity. 
The first bottleful of the gas may well be rejected as impure. Remove 
the end of the delivery-tube from the water, or, better still, break the 
connection before removing the lamps. Why ? 

As soon as it is convenient, fill one of the larger gas-hold3rs with oxy- 
gen. For this purpose it will be better to use larger quantities of the 
materials. A retort made of large gas-pipe and expressly constructed 
for the purpose is desirable in every laboratory (see Appendix, § 21). 

30. Preparation. — Oxygen was produced in Experi- 
ment 13, and it is often prepared in large quantities by 
this method ; small quantities are most conveniently pre- 
pared by Priestly's method, as in Experiment 29. The 
best method of making considerable quantities of oxygen 
for laboratory experiments, and the method by which it is 
usually prepared for commercial purposes, is by heating 
potassium chlorate as in Experiment 30. If the tempera- 



OXYGEN. 37 

ture is high enough, manganese dioxide can be reduced to 
a lower oxide of manganese, with the evolution of oxygen. 

When barium peroxide (Ba0 2 ) is heated to 700° under 
diminished pressure it is reduced to barium oxide (BaO) ; 
i.e., it gives up part of its oxygen. When heated in air 
under an increased pressure, this barium oxide takes up 
ox} r gen from the air, and is thus changed back to the 
peroxide, which may be thus used repeatedly. By con- 
tinuing such a process, oxygen is sometimes prepared for 
commercial purposes. 

Oxygen may be prepared without the use of heat by 
the action of dilute hydrochloric acid on a mixture of 
barium peroxide and manganese dioxide. For this purpose, 
mix fifty grams of barium peroxide and twenty-five grams 
of manganese dioxide. Place this mixture in' a flask simi- 
lar to that shown in Fig. 7, slowly add the dilute acid, 
and collect the gas over water. Small quantities of 
oxygen may be quickly prepared without the use of heat 
by the action of water on sodium peroxide. For this 
purpose, a dropping tube will be found convenient. 

As will soon appear, air is a mechanical mixture of two 
gases, ox} 7 gen and nitrogen, and may be liquefied by high 
pressure at a low temperature. As liquid nitrogen boils at 
a lower temperature than oxygen does, when the liquefied 
air is allowed to evaporate, the nitrogen passes off in the 
first portion and leaves nearly pure oxj^gen behind. This 
process is also used on the commercial scale. 

31. The Reactions. — In the preparation of oxygen from 
mercuric oxide, the latter is decomposed into its constituent 
elements : 2HgQ + heat = 2Hg + Q ^ 



38 WATER AND ITS CONSTITUENTS. 

At the end of the process described in the preparation 
of oxygen from potassium chlorate, the ignition-tube 
contained manganese dioxide and potassium chloride 
(KC1). This chloride is easily soluble in water ; the 
dioxide is not. After the tube has cooled, all of the 
manganese dioxide may be recovered unchanged by 
agitating the solid residue from the tube with water, and 
filtering. The dioxide suffered no permanent chemical 
change and was used only because, in some way for which 
no satisfactory explanation has yet been given, it caused 
the chlorate to decompose more quietly and at a lower 
temperature. This effect, produced by what seems to be 
the mere presence of a substance, has been called catalysis. 

2KC10 3 + 2Mn0 2 -f heat = 2KC1 -f 2Mn0 2 + 30 2 , 

or 2KC10 3 -I- heat = 2KC1 -f 30 2 . 

In the preparation of oxygen by decomposing manganese 
dioxide at a high temperature, the changes may be repre- 
sented thus : _ ^ , ,, ^ _ 
3Mn0 2 -f heat = Mn 3 4 -4- 2 . 

In the preparation of oxygen by heating barium peroxide, 
the chemical reactions may be represented thus : 

2BaG 2 (under reduced atmospheric pressure) -f- heat 
(lull red) = 2BaO + 2 . 

2BaO (in air under increased pressure) + 2 -f heat = 
2Ba0 2 . 

Note. — The relations that exist between chemical action nnd 
heat have been recognized in the equations given in § 24 and £ 31, 
and elsewhere in this book. As a full consideration of thennochemical 
phenomena would lead beyond the proper limits of an elementary 
course, no attempt will be made in these pages to do more than 
occasionally to call attention to them. See § 145. 



OXYGEN. 39 

32. Physical Properties. — Oxygen is a transparent, col- 
orless, tasteless, odorless gas, not to be distinguished by 
its appearance from hydrogen or from ordinary air. One 
liter of it (under ordinary conditions of temperature and 
atmospheric pressure) weighs 1.4291 grams. As it is 
about one-tenth heavier than air, it may be collected 
by downward displacement, but it is more satisfactorily 
collected over water. It is sparingly soluble in water. 
Like hydrogen, it may be liquefied by subjecting it to 
high pressure and low temperature. Liquid oxygen has 
a light blue color and, under ordinary atmospheric press- 
ure, boils at - 181°. 

Chemical Properties of Oxygen. 

Note. — The bottles containing the oxygen for the experiments 
immediately following should be prepared by grinding their lips flat 
with emery powder, as described in Appendix, § 5, h. Have ready 
several greased glass plates with which to close the mouths of the 
bottles thus prepared. During the combustions, it will be well to 
keep the mouths of the bottles covered loosely, as with cardboard. 

Experiment 31. — Repeat Experiment 15, holding the bottle right 
side up, and allow the taper to burn until the flame dies out. ~ 

Remove the taper and cover the mouth of the bottle. Label 
the bottle "Xo. 1." 

Experiment 32. — Into a second bottle of the gas, thrust a 
splinter of dry wood having a glowing spark at its end. When 
aflame, withdraw it, blow out the flame, and repeat until the 
gas fails to rekindle the splinter. This is one of the best tests 
for oxygen. Cover the mouth of the bottle. Label this bottle 
" Xo. 2." 

Experiment 33. — Place a lighted candle on a stand between FlG - 17 * 
two boys, A and B. Let B fill his mouth with oxygen from the gas- 
holder. A may blow out the flame, leaving a glowing wick ; B may 
then puff oxygen upon the wick and relight it. Repeat the experiment 
until the mouthful of oxygen is exhausted. B need not inhale the 
oxygen, but if a little does get into his lungs it will do no harm. 



40 



WATER AND ITS CONSTITUENTS. 



Note. — If convenient, perform the next five experiments in a 
darkened room. 

Experiment 34. — Around a bit of charcoal, wind one end of a fine 
wire, to form a handle. Have ready a bottle containing a liter or 
more of oxygen. Ignite the charcoal at the lamp 
and thrust it into the bottle. Brilliant combustion 
will take place and continue until all of the char- 
coal, or all of the oxygen, is consumed. Cover the 
bottle as before, and label it " No. 3." 




Fig. 18. 



Experiment 35. — Place a bit of sulphur (brim- 
stone) the size of a pea into a deflagration spoon 
(see Appendix, § 19) and hold it in the lamp-flame. 
It will melt and then take fire. While burning, 
thrust it into a good-sized jar of oxygen. It will 
burn with a beautiful blue flame and much more brilliantly than it 
did in the air. At the end of the experiment, cover the jar and label 
it " Xo. 4." 

Experiment 36. — A larger glass vessel is desirable for this experi- 
ment. A good-sized bell-glass, such as is used in air-pump experiments, 
or a globe, such as is used for keeping gold-fish, will answ T er well. In 
the middle of a large plate or tray con- 
taining water 4 or 5 cm. deep, place a 
metal support rising several centimeters 
above the surface of the w r ater. From a 
stick of phosphorus, cut, under ivctter, a 
piece the size of a large pea, dry it 
thoroughly between pieces of blotting- 
or filter-paper, place it upon the support 
in the tray, ignite it witli a hot wire, 
and quickly invert over it the vessel of 
oxygen. The combustion is exceed- 
ingly energetic and brilliant. The metal 

support for the phosphorus may be protected from combustion by 
coating its upper surface with lime, chalk,, or plaster of Paris. At 
first, part of the gas may bubble out at the mouth of the vessel, but 
as the dense fumes formed by the burning of the phosphorus are 
absorbed, water will rise within the vessel. Then pour more water 
into the tray, if necessary to preserve the seal, and label the globe 
" No. 5." 



1 

m. - 1 



Fig. 19. 



41 



Experiment 37. — Form a spiral of fine iron wire (piano-forte wire 
is preferable, but a single strand of ordinary wire picture-cord will do 
well) by winding the wire upon a lead pencil or a piece of glass tubing ; 
wind some waxed thread upon the lower end.of the wire, or dip the end 
of the wire into melted sulphur so that a small sulphur bead shall adhere 
to the wire. At the bottom of a vessel containing two or three liters of 
oxygen place a layer of water or of sand. Ignite the thread or sulphur 
and quickly place the wire in the oxygen. The burning wax, or 
sulphur, heats the end of the 
wire to redness. The wire then 
burns with beautiful scintilla- 
tions. The experiment may be 
made more brilliant by using a 
coiled watch-spring instead of 
the iron wire. The watch- 
spring, which may be had gratis 
of almost any jeweler, is to be 
softened by heating it to redness 
and allowing it to cool slowly; 
it may then easily be coiled. 
Wind the lower end of the 
spring with twine and dip it 
into melted sulphur, to prepare 
the kindling material. The 
kindling matter should be no 
larger in quantity than is neces- 
sary to heat the wire or spring to the necessary temperature ; any 
excess interferes with the success of the experiment, by consuming 
the free oxygen and forming undesirable compounds in the jar. The 
melted metal globules sometimes fuse their way into or through the 
. bottom of the jar, when the water or the sand is not provided to pre- 
vent such a result. 

Experiment 38. — Blow a jet of oxygen into the flame of an alcohol- 
lamp. In the flame thus produced hold a piece of watch-spring or of 
steel wire. It will burn with brilliant scintillations. 

Experiment 39. — Into bottle No. 1, put a piece of moistened blue 
litmus-paper ; it will be reddmed. Now pour in a little clear lime- 
water (slacked lime dissolved in water; see Experiment 56), cover the 
mouth of the bottle tightly with the palm of the hand and shake 




42 WATER AND ITS CONSTITUENTS. 

the bottle vigorously ; a partial vacuum will be formed and the clear 
lime-water will become turbid and yield a white precipitate. The 
reddening of the blue litmus-paper shows the presence of <in acid. 
The colorless gas formed .by the burning of the taper in oxygen has 
united with the water to form an acid. What is this colorless gas? 
The turbidity of the lime-water and the precipitate show that it is 
carbon dioxide (C0 2 ), sometimes called carbonic anhydride, or car- 
bonic acid gas. The carbon of the taper united with the oxygen. 

c + o 2 = co 2 . 

Experiment 40. — Try the contents of jars 2 and 3 with a lighted 
taper. The flame is extinguished as promptly as it would be by water. 
Numerous gases act in this way. We have seen that hydrogen ex- 
tinguishes flame ; but this gas is not kindled as we know that hydro- 
gen would be. Try the contents of the jars with moistened blue 
litmus-paper. The paper is reddened. Have you any idea of what 
the gas is ? Try the gas with clear lime-water. We have the turbidity, 
etc., as before. What do you now think the gas is? The dry wood 
burned in No. 2 was largely carbon, and the charcoal burned in Xo. 3 
was nearly pure carbon. In either case, 

C + 2 = C0 2 . 

Experiment 41.^ Test the contents of jar Xo. 4 with a lighted 
taper. The flame is promptly extinguished as before. Test with 
the moistened blue litmus-paper. The paper is reddened as before. 
What does this reddening show? Do?s the jar contain hydrogen? 
Does it contain oxygen? Do you think that it contains carbon 
dioxide ? Why ? Test with clear lime-water. Does it contain carbon 
dioxide? How was this gas formed? Was any carbon used in its 
production? The gas is sulphur dioxide (S0 2 ) sometimes called 
sulphurous anhydride. s -I- () — SO 

Note. — If we turn to jar Xo. 5 we shall find that the phosphoric 
oxide (P 2 O s ) formed by the combustion of the phosphorus was dis- 
solved in the water. If this water is tested with blue litmus-paper 
it will be found to have acid properties. We have thus formed 
oxides of carbon, of sulphur and of phosphorus, and seen that these 
oxides unite with water to form acids. If the litmus-paper 
used in testing these gases had been dry instead of wet it would not 
have been reddened. The oxide of iron (FeX) 4 ) formed in Experi- 
ment 37 is solid and insoluble in water. 



OXYGEN. 43 

33. Chemical Properties. — As illustrated in the pre- 
ceding experiments, oxygen gas is chiefly marked by great 
chemical activity. In each case, the substance ignited in 
the oxygen united with it chemically, forming a com- 
pound called an oxide. Thus, an oxide is the product 
of the chemical union of oxygen with another element. 
Oxygen enters into combination with all the elements 
except fluorine, helium, and argon. 

Oxygen unites directly with most substances with suf- 
ficient energy to produce light and heat. In the ordinary 
use of the term, combustion is chemical union with oxygen 
with such attending phenomena. 

Liquid oxygen has a chemical activity even more vigor- 
ous than that of the gas, and has been used with oxidizable 
substances as an explosive. For instance, felt and similar 
substances, when moistened with liquid oxygen or liquid 
air, explode violently upon ignition. Such explosives 
have the advantage of becoming safe upon the evapo- 
ration of the liquid. 

Note. — In the periodic system of the chemical elements (§ 148, b), 
oxygen falls in Group 6, the other members of which are considered 
in Chapter XVI. 

34. Uses. — Oxygen is used in countless ways in the 
laboratories of nature and of man. It is essential to the 
processes of animal respiration, ordinary combustion, fer- 
mentation, and decay. It is used in the arts to increase 
the intensity of combustion for purposes of heat and light. 
If nearly pure oxygen could be made so cheaply that it 
might be used for the combustion of coal in furnaces, and 
for other chemical operations, such use would result in the 
material cheapening of many industrial processes. Be- 



44 WATEK AND ITS CONSTITUENTS. 

cause of its relation to respiration and combustion, oxygen 
is probably more commonly and constantly used than any 
other substance, certainly more than any other element. 
Its great importance in these connections will be more 
fully explained in the chapter on the atmosphere. 

(a) When oxygen is needed in considerable quantities, it may be 
bought under high pressure in steel cylinders in which it may be kept 
indefinitely, and from which it may be drawn out as required. 

Tests for Oxygen. 

Experiment 42. — Into a large test-tube filled, over water, with nitric 
oxide (NO, see § 70) pass a small quantity of oxygen. The two color- 
less gases combine eagerly, forming dense red fumes that are rapidly 
dissolved in the water. 

Experiment 43. — Dissolve a piece of potassium hydroxide (caustic 
potash, KOH) the size of a pea, in 10 cu. cm. of water and pom - the 
solution into a long test-tube filled with oxygen. Add a few flakes of 
pyrogallic acid. Close the mouth of the tube with the thumb and 
shake the contents. The liquid will be blackened. Place the mouth 
of the tube under water and remove the thumb. Water will rise 
in the tube to fill the partial vacuum formed by the absorption of the 
oxygen in the tube by the liquid mixture. 

35. Tests. — Free oxygen, not much diluted with other 
gases, is most easily tested by plunging into it a glowing 
splinter, as in Experiment 31. TI13 only other gas that 
will thus rekindle the splinter is nitrous oxide (laughing 
gas, N 2 0). This test, though generally enough, is not 
conclusive except in the known absence of nitrous oxide. 
When oxygen is mixed with nitric oxide (NO), the two 
colorless gases unite at ordinary temperatures to form a 
reddish brown gas, nitrogen peroxide (N0 2 ). Another 
test for oxygen is its action on an alkaline solution of 
potassium pyrogallate, with which it unites chemically to 



OXYGEN. 45 

produce the brown compound with which fingers are often 
stained in photographic work. This test is commonly 
used to determine the amount of oxygen present in a 
mixture of gases containing it. 

Ozone. 

Experiment 44. — Prepare a cylinder of phosphorus three or four 
centimeters long, by scraping its surface clean under water. ( Remem- 
ber the caution preceding Experiment 5.) Place the phosphorus in 
a clean bottle of one or two liters capacity, and pour in enough water 
to half cover the cylinder. Close the mouth of the bottle with a plate 
of glass or a loose stopper, and set the bottle in a warm place (20° or 
30°). In 10 or 15 minutes, notice the fog above the phosphorus. 
Allow the bottle to remain for several hours. The feeble, chlorine- 
like odor of ozone will be discernible. A still more convenient 
method is to place a few drops of ether in a tall beaker, and to stir 
the quickly formed vapor with a hot glass rod. 

Experiment 45. — Prepare two slips of white paper by dipping them 
into a solution of starch and potassium iodide (see Experiment 
102). Thrust one of these into a bottle of oxygen ; no change will 
be noticed. Thrust the other test-paper into a bottle or beaker con- 
taining ozone ; the white paper will be promptly colored blue. The 
energetic ozone displaces the iodine. 

2 KI + 3 = K 2 + 2 + T 2 . 

The free iodine colors the starch blue. See Experiment 132. 

36. Ozone. — In addition to the ordinaiw form of 
oxygen, which contains two atoms in each molecule, a 
remarkable variety is known in which there are three 
atoms to each molecule. This condensed and more active 
form of oxygen is called ozone. In changing oxygen to 
ozone there is a volumetric condensation of one-third. 
Ozone is formed at the + electrode in the electrolysis 
of water ; by the discharge from an electric machine 
through air or oxygen ; or by the slow oxidation of phos- 



46 WATER AND ITS CONSTITUENTS. 

phorus in moist air, etc. It is best prepared by electric 
apparatus devised for that purpose. 

37. Properties of Ozone. — Ozone is one of the most 
powerful oxidizing agents known. It is probably present 
in pure country and sea air, and is noticeably absent in 
the atmosphere of large cities, where its oxidizing influ- 
ence upon organic and other deleterious matter results 
in partial disinfection and its own transformation into 
oxygen and oxygen compounds. It has a highly pene- 
trating odor. It is so energetically oxidizing that, if 
breathed continuously, it produces a corroding action on 
the throat and lungs. Unlike ordinary oxygen, ozone, 
especially when moist, oxidizes strongly at ordinary tem- 
peratures. For this reason, it is one of the most valuable 
disinfectants and purifiers. 

Ozone may be detected by its odor in the air near a 
dynamo or an electric motor that is sparking, as in 
starting a loaded electric car. In its oxidizing action, 
its volume is supposed to undergo no change, the 
third atom of the ozone molecule (0 3 ) entering into 
combination and leaving the two atoms of the ordinary 
oxygen molecule (0 2 ). It is changed by heat into 
ordinary oxygen, with increase of volume. 

38. Allotropism. — Although ozone manifests charac- 
teristics decidedly different from those of ordinary oxy- 
gen, its fundamental, chemical identity with oxygen is 
unquestionable. For example, the potassium oxide (K 2 0) 
that it formed by displacing the iodine of the potassium 
iodide, in Experiment 45, is identical with the potassium 
oxide formed in any other way. This capability of exist- 



COMPOUNDS OF HYDROGEN AND OXYGEN. 47 

ing in different physical forms ivith chemical identity unde- 
stroyed is called allotropism or allotropy. Ozone is an 
allotropic modification of oxygen. 

EXERCISES. 

— 1. How may Nature be questioned? 

—2. Judging only from the names, which is the richer in oxygen, 
phosphorous acid or phosphoric acid ? 

- 3. Suppose that the hydrogen of sulphuric aci'd is replaced with 
potassium; give the name of the resultant compound and of the class 
to which it belongs. 

— 4. How many kinds of atoms are there in calcium oxide? In 
calcium carbonate? 

-5. State a characteristic difference between chemical energy and 
gravitation. 

~6. "What is the chemical difference between sheet zinc and 
granulated zinc? 

~ 7. How is a gas collected over water? 

— 8. What property of hydrogen enables us to transfer it from one 
vessel to another by upward decantation ? 

— 9. How may hydrogen be freed from moisture? 

— 10. What is the chemical difference between 2 and 3 ? 

IV. COMPOUNDS OF HYDROGEN AND OXYGEN. 

39. Combustion of Hydrogen. — When hydrogen is heated 
to the temperature of about 500°, in the presence of free 
oxygen, the two elements enter into chemical union, form- 
ing water (H 2 0). This was shown in a general way 
in Experiment 28. Whatever the conditions under which 
hydrogen is burned in oxygen or in air, the sole product is 
water. This is true, even in the combustion of a hydrogen 
compound. 2 H 2 + 2 = 2H 2 0. 

As oxygen is sixteen times as heavy as hydrogen, the 
gravimetric composition of water is eight parts of oxygen 
to one of hydrogen. See § 141 (<?). 



48 



WATER AND ITS CONSTITUENTS. 



40. The Compound Blowpipe. — The compound or oxy- 
hydrogen blowpipe consists of a double tube, one inside 
the other. The interior tube is connected by rubber 

tubing with the oxygen 
gas-holder; the outer tube, 
with the hydrogen gas- 
holder. Hydrogen is first 
turned on and ignited at a. 
Oxygen is then turned on 
until the flame is reduced to a fine pencil. The pressure 
at the gas-holders should be steady, the amount thereof 
being easily determined by trial. 




The Combustion of Hydrogen. 

Experiment 46. — Hold bits of iron and of copper wires, watch- 
springs, strips of zinc, etc., in the flame of the compound blowpipe. 
They will be readily dissipated with characteristic luminous effects. 
A fine wire of platinum, an exceedingly refractory metal, is readily 
melted, and silver can be thus distilled. A piece of lime or of chalk, 
freshly scraped to a point and held in the flame, is heated to such a 
high degree of incandescence that it produces a light of*remarkable 
intensity. This is essentially the Druinmond or calcium light. 

Experiment 47. — Over the jet, a, of the compound blowpipe, slip a 
piece of rubber tubing. AVith both gases flowing, dip the tubing into 
a metallic dish full of soap- 
suds until a mass of foam 
has formed. Close the stop- 
cocks at the gas-hold ers or 
at the blowpipe, remove the 
tubing from the soap-suds, 
and then touch the foam 
with a flame carried at the 
end of a stick about a meter 
in length. A violent explosion will take place, 
Experiment 20.) 




(See note following 



COMPOUNDS OF HYDROGEN AND OXYGEN. 



49 



Note. — If you have no compound blowpipe, introduce one volume 
of oxygen and two of hydrogen into a gas-bag or a small gas-holder 
(see Appendix, § 14). The gases will soon become thoroughly mixed 
by diffusion, when they may be passed into the soap-suds through the 
rubber tubing. Remember that this mixture is dangerously explosive ; 
be sure that there is no possibility of fame coming into contact ivith the con- 
tents of the gas-bag or of the connected tubing. The explosion just 
described was free from danger, because the restraining wall of the 
explosive mixture was only a thin film of water, the flying fragments 
of which could do no harm. If the contents of your gas-holder should 
explode, the flying fragments would probably do serious damage. It 
is advisable to throw away the mixed gases that may remain at the 
close of the experiments with them. Any attempt to burn these gases 
previously mixed, even as they issue from the jet of the compound 
blowpipe, will result in an explosion. 

Experiment 48. — Repeat Experiment 26, using the mixed gases 
instead of hydrogen, and guarding carefully against an accidental 
explosion. The bubble, or a mass of bubbles dipped from the dish 
shown in Fig. 22, may be safely exploded while resting in the palm of 
the hand. 

Experiment 49. — Support a w T ide tube of clear glass in a vertical 
position. A bottomless bottle, the neck of a broken retort, or a lamp- 
chimney will answer well. Through 
the perforated cork that closes the 
upper end, pass a stream of hydrogen 
from the gas-holder. When the air 
has been driven out of the bottle, 
apply a flame at the lower end and 
regulate the flow so that the gas burns 
slowly at the opening. From another 
gas-holder pass a current of oxygen 
through a piece of glass tubing drawn 
out to form a small jet. As the jet 
passes through the burning gas, the 
oxygen takes fire and burns in an 
atmosphere of. hydrogen. 




Fig. 23, 



41. The Eudiometer. — The eudiometer is an instru- 
ment for determining the proportions in which gases 



SCHOOL CHEMISTRY- 



50 



WATER AND ITS CONSTITUENTS. 




unite. It consists of a strong glass tube with two plati- 
num wires fused into the sides near the closed end. The 
wires nearly touch within the tube. One 
of the most common forms consists of a 
U-tube with the closed arm, 5, graduated 
to cubic centimeters. 

Volumetric Composition of Water. 

Experiment 50. — Fill the eudiometer with 
water and hold it with the open arm, a, hori- 
*ig. 24. zontal, under water and under the closed arm, b. 

By means of a rubber tube carrying a short piece of glass tubing 
drawn out to a fine jet, pass about 20 cu. cm. of pure oxygen from the 
gas-holder into b. Be sure that the air had been previously driven 
out of the delivery-tube ; make the measurement with the eudiometer 
erect and the water standing at the same level in both branches. 
Water may be removed from a, if necessary to this end, by means of 
a pipette (see Appendix, § 6). Now introduce about 50 cu. cm. of 
pure hydrogen into b, and note the exact amount of gas therein as 
before. It may prove difficult to introduce exactly 20 and 50 cu. cm. 
A little variation matters not, provided that you measure accurately 
the amounts actually introduced, and that the volume of the hydrogen 
is more than twice that of the oxygen. Suppose that the first meas- 
urement shows 21 cu. cm. of oxygen, and that the second shows 
75 cu. cm. of mixed gases. Then you have introduced 54 cu. cm. of 
hydrogen. Close the open end firmly with the thumb, leaving a 
cushion of air between it and the surface of the water, as shown in 
Fig. 24. Produce an electric spark between the ends of the platinum 
wires in the mixed gases. The spark produces combination between 
the oxygen and part of the hydrogen. On removing the thumb and 
bringing the liquid surfaces to the same level, it will be found that 
there are only 12 cu. cm. of gas in b. By filling a with water and 
closing it with the thumb, the gas may be easily passed from b into a, 
and thence, under water, to a convenient vessel for testing. It will 
be found to be hydrogen. The 21 cu. cm. of oxygen has united with 
42 cu. cm. of hydrogen to form a minute quantity of water, leaving 
the 12 cu. cm. of hydrogen because there was no oxygen with which 
it could unite. 



COMPOUNDS OF HYDROGEN AND OXYGEN. 



51 



42. Volumetric Composition of Water. — If in the pre- 
ceding experiment the eudiometer had been kept at a 
temperature above 100°, and the gases confined by mer- 
cury instead of water, b would have contained forty-two 
cubic centimeters of steam and twelve cubic centimeters 
of Irydrogen. The volume of steam would be the same 
as that of the hydrogen that entered into its composition. 
The combination was accompanied by a diminution of 
volume equal to that of the oxygen entering into chemical 
union. In other words, three volumes shrink to two vol- 
umes in the process of combination. Representing equal 
volumes of the gases by equal squares, the volumetric com- 
position of water and the condensation just mentioned 
may be represented to the eye as follows : 



H 

l 


+ 


H 

1 


+ 


O 

16 


= 


H2O 

18 




W 


ate: 


r Test* 


j. 





Experiment 51. — Provide three samples of water; one of clean, 
fresh rain-water, one from the city or household supply, and one 
that is known to be contaminated. Put a portion of each sample 
into separate test-tubes that are clean, add to each a few drops of 
nitric acid and then a few drops of a solution of silver nitrate. 
Compare the quantities of precipitate formed in the several tubes. 
This is a test for chlorides, and is used here because animal refuse 
is always accompanied by salt, which is a chloride. 

In like manner, place about 100 cu. cm. of each of the sample 
waters in clean test-tubes. To each, add, drop by drop, a dilute 
solution of potassium permanganate, shaking the tube after the 
addition of each drop. Count the drops added until a faint pink 
color remains after a few minutes. The permanganate is destroyed 
by animal or vegetable matter in solution. The number of drops 
required to produce a permanent pink color is a rough measure of 
the degree of contamination. 



52 WATER AND ITS CONSTITUENTS. 

In separate porcelain dishes, on a steam bath (a beaker containing 
boiling water will answer), evaporate to dryness about 101) cu. cm. of 
each of the sample waters. When the residue is quite dry, carefully 
heat each dish over a gas- or an alcohol-flame until the residue begins 
to char. Observe the odor evolved. The residue from a pure water 
will be white, and will not evolve a disagreeable odor on charring. 

43. Contaminated Waters. — Like oxygen, water is es- 
sential to the existence of animal life. It is universally 
present in the air, in the ground, and in animal and vege- 
table tissues. As it occurs in nature, it is never pure, 
fresh rain-water approaching most nearly to purity. 
Clearness alone does not indicate purity, as the most 
common impurities are held in solution. These dissolved 
impurities are commonly mineral salts, but they may con- 
sist of animal and vegetable substances. 

The mineral substances in solution are smallest in 
natural waters derived from springs in regions of granite 
rocks, and highest in waters from limestone formations. 
When water is used in boilers for steam making, these 
mineral salts separate as the water is evaporated, and 
either form a muddy sediment in the boiler or adhere 
firmly to the flues and walls of the boiler, forming boiler- 
scale. See § 184:. 

Because of the animal and vegetable substances dis- 
solved in it, water may become one of the most danger- 
ous carriers of contagious diseases. The germs that cause 
these diseases feed on these dissolved substances and, 
under favorable conditions of temperature, multiply with 
great rapidity. For this reason epidemics of typhoid 
and similar diseases are often spread by the use of con- 
taminated drinking water. When, for any reason, water 
is suspected of contamination with animal refuse, or, 



COMPOUNDS OF HYDROGEN AND OXYGEN. 53 

better still, until it has been proved free from all such 
contamination, it should not be used for drinking unless 
it has been boiled a quarter of an hour or more. The 
organisms that cause these diseases are killed by the tem- 
perature of boiling water, so that, unless subsequently 
contaminated, boiled water is free from this danger. 

It may often be ascertained whether waters contain 
animal contamination by the fact that such waters give a 
white cloudy precipitate with a solution of silver nitrate, 
decolorize a dilute solution of. potassium permanganate, 
and, when evaporated to dryness, leave a residue that 
blackens and emits a disagreeable odor when heated with 
a flame. 

(a) The roost perfect purification of water is secured by distilla- 
tion. This process is largely used at sea, but it is not easily availa- 
ble for domestic purposes. The " flat " or vapid taste of boiled or 
distilled water may be removed by passing the water through a filter 
thus exclusively employed. Filtration affords a valuable but not 
complete protection against bacterial diseases, and the process is 
largely employed for both individual and public water-supply. 

(b) Many natural waters act upon the lead of pipes through 
which they are conveyed, forming poisonous compounds. Lead pipes 
used for such purposes should be tin-lined. 

44. Hydrogen Dioxide. — Hydrogen dioxide (H 2 2 ) is 
generally prepared by the action of dilute sulphuric acid 
on barium dioxide : 

Ba 2 + H 2 S0 4 = BaS0 4 + H 2 2 . 
It is a syrupy, colorless liquid and, when rapidly heated, 
separates into water and oxygen with almost explosive 
violence and the liberation of heat. It may be considered 
as composed of two groups of OH ; thus, (HO)-(OH). 
This atomic group, OH, is called hydroxyl. Hydrogen 



51 WATER AND ITS CONSTITUENTS. 

dioxide is sometimes called free hydroxyl. It is used 
as an oxidizing agent, as a disinfectant and germicide, 
and for bleaching hair. 

EXERCISES. 

1. What is the difference between a chemical and a physical 
change? Make your answer as explicit as you can, and illustrate it. 

2. (a) Describe briefly the common method for the preparation of 
oxygen, omitting no essential. (J>) Tell what you can of hydrogen 
and its preparation. 

3. (a) Give the symbol and chemical properties of oxygen. 
(7>) What is meant by oxidation*? 

4. («) What is an element ? (/>) How many are known ? (c) What 
gases enter into the composition of water? (d) Prove your answer 
in two ways, one method being the reverse of the other, (e) What 
name do you give to each method? 

5. When a current of steam is passed through an iron tube nearly 
filled with bright iron-turnings or filings, the tube being placed across 
a furnace and its middle portion heated to redness, large quantities of 
a combustible gas that may be collected over water are delivered from 
the tube, (a) What do you suppose the gas to be? Why? (h) Will 
the iron-turnings in the tube weigh more or less at the end of the 
experiment than they did at the beginning? Why ? 

6. How many hydrogen oxides are known? Name them. Define 
chemistry. 

7. What is the distinction between a mixture and a compound? 

8. (a) If 240 cu. cm. of hydrogen and 120 cu. cm. of oxygen are 
made to combine, what will be the name of the product? (b) If the 
experiment is performed in a vessel having a temperature above that 
of boiling water, what will be the name and volume of the product? 

9. If 300 cu. cm. of steam are condensed to water and the water is 
decomposed, what will be the volume and composition of the product? 

10. («) What weight of hydrogen is there in 8064 grams of water? 
(b) What volume of hydrogen ? 

11. Describe the potassium permanganate test for the purity of 
water. 

12. How could you tell oxygen from hydrogen ? 

13. State the principal difference between ordinary oxygen and its 
allotropic modification. 



CHAPTER III. 

AIR AND ITS CONSTITUENTS. 

I. AIR. 

45. Occurrence. — The earth is surrounded by an at- 
mosphere of air extending to a height variously estimated 
at from fifty to two hundred miles. 



* Composition of the Air. 

Experiment 52. — Repeat Experiments 42 and 43, using common air 
instead of oxygen. These tests show the presence of free oxygen in 
the air. 

Experiment 53. — Provide a cork about 5 cm. in diameter and 2 cm. 
in thickness. Cover one side with a thin layer of plaster of Paris 
mixed with water. The paste may be raised near the edge of the 
cork so as to produce a concave sur- 
face. Dry the cork thoroughly and 
you have a convenient capsule for 
floating upon water. For a single 
experiment, the cork may be covered 
with dry powdered chalk or lime. 
Notice the "Caution" on page 15. 
Upon this capsule, place a piece of 
phosphorus that has been dried by 
wrapping it in blotting- or filter- 
paper. Float the capsule upon water 
in a pan, ignite the phosphorus with 
a hot wire, and cover it with a bell-glass or other wide-mouthed 
vessel. The water in the pan should seal the mouth of the bell-glass 
so as to exclude the external air. While the phosphorus is burning, 
hold the bell-glass down with the hand. The phosphorus combines 
55 




Fig. 25. 



56 AIR AND ITS CONSTITUENTS. 

with the oxygen of the air, forming dense fumes of phosphoric oxide 
(P2O5). These fumes are soon absorbed by the water, which rises 
in the bell-glass to occupy the space vacated by the oxygen. As the 
water rises in the bell-glass, pour water into the pan as may be neces- 
sary to preserve the seal. If any phosphorus remains at the end of 
the experiment, be sure that it is burned up. 

Experiment 54. — When the fumes of P 2 5 have been absorbed, 
slip a glass plate under the mouth of the bell-glass and place it mouth 
upward, without admitting any air. If the bell-glass is capped, as 
shown in Fig. 25, it need not be removed from the water-pan ; water 
should be poured into the pan until the liquid outside the receiver is 
at the same level as that inside. Test the gaseous contents with a 
lighted taper. The flame is extinguished, but the gas does not burn. 
It is neither oxygen nor hydrogen. It is nitrogen, an element that 
we shall study in the next section, and was left behind when the 
oxygen of the air united with the phosphorus. 

Experiment 55. — To show approximately the quantitative compo- 
sition of the atmosphere, pour into a graduated tube 10 cu. cm. 
of a solution of 3 grams of potassium hydroxide (caustic potash) 
in 1 gram of pyrogallic acid. Close the tube air-tight with a rubber 
stopper, and note the volume of the air in the tube. Shake the tube 
gently for about five minutes, and then remove the stopper under 
water. Carefully raise the tube, keeping its mouth under water, 
until the water inside and outside the tube are at the same level. 
The free oxygen in the confined air has been absorbed by the pyro- 
gallate solution. The residual gas is nitrogen. Its volume is about 
four-fifths that of the air confined at the beginning of the experiment. 

46. Composition of Air. — Air is composed chiefly of 
oxygen and nitrogen. Very careful determinations show 
its percentage composition to be about as folloAvs : 

By Volume. By Weight. 

Oxygen 21 23 

Nitrogen 79 77 

100 100 

This composition of the air is nearly but not quite con- 
stant at different times and places. The air also contains 
small quantities of carbon dioxide, more or less watery 



AIR. 57 

vapor, and traces of ammonia, hydrogen, sulphur gases, 
nitrogen acids, and several elementary gases of which not 
much is known. See § 58. 

47. Physical Properties. — The air, when pure, is trans- 
parent, colorless, tasteless, and odorless. It is 14.45 times 
as heavy as hydrogen. It may be liquefied by intense 
pressure at a very low temperature. The liquid air may 
even be frozen. As the boiling point of nitrogen (— 194°) 
is lower than that of oxygen (— 183°), the nitrogen vola- 
tilizes first when the liquid is slowly warmed, leaving 
nearly pure oxygen behind. Liquid air has large com- 
mercial and industrial possibilities. 

48. Chemical Properties. — The chemical properties of 
air are those of its several constituents. Its oxygen sup- 
ports combustion, the energy of the combustion being 
checked by the diluting nitrogen. Its nitrogen manifests 
all the properties of nitrogen. Its watery vapor con- 
denses when the temperature falls, just as any other 
watery vapor would do. Hence, we have dew and frost. 
When a stream of air is passed through lime-water, its 
carbon dioxide renders the clear liquid turbid, just as 
carbon dioxide always does. 

49. Air is a Mixture. — The first sentence in the pre- 
ceding paragraph intimates that the constituents of our 
atmosphere are not chemically united but merely mixed ; 
that each of them is free. This fact is shown by the fol- 
lowing additional considerations : 

(a) When the constituents are mixed in the proper proportions 
they form air, but there is no change of volume or manifestation of 
heat, light, or electricity. 



58 AIR AND ITS CONSTITUENTS. 

(b) The composition of air is slightly variable. 

(c) Each gas dissolves in water independently of the other. When 
water is boiled, it loses the gases it held in solution. Of these gases, 
32 parts in 100 are oxygen and 68 parts are nitrogen. The water 
absorbed oxygen just as if there was no nitrogen present; it absorbed 
nitrogen just as if no oxygen was present. This increased richness 
in oxygen is of vital importance to fishes. If the constituent gases 
were chemically united, they would be absorbed by water in the 
proportion stated in § 46. 

(d) The gases do not unite in any simple ratio of their atomic 
weights. As will be seen subsequently, this is a very important 
consideration. 

50. Oxidation. — Combustion is the rapid union of other 
substances with oxygen. When the fire burns, oxygen 
from the air is uniting with the coal or other fuel to pro- 
duce carbon dioxide and water. All decay of vegetable 
and animal substances is a similar but much slower pro- 
cess, so slow that the heat produced is not noticed. In 
general, decay is brought about by the action of bac- 
terial organisms. When such substances are perfectly 
sterilized, they remain intact as long as kept sterile. 
The rusting of metals is also a process of oxidation, the 
rust being an oxide of the metal. 

(«) Since all ordinary combustion takes place in air, which fur- 
nishes the necessary supply of oxygen, it is customary to speak of 
oxygen as a supporter of combustion, and the hydrogen or other sub- 
stance that thus unites with the oxygen as a combustible. 

A Product of Animal Respiration. 

Experiment 56. — Put a piece of fresh lime about the size of a hen's 
egg into a pitcher and upon it pour a small teacupful of water. When 
the lime has crumbled, pour a pint or so of water into the pitcher and 
stir the contents thoroughly. Let the turbid mixture stand until it 
settles, and then half fill a clear tumbler with the clear liquid. Fill 



AIR. 



59 



the lungs with air. Slowly breathe through a tube so that air from, 
your lungs bubbles up through the lime-water in the tumbler. The 
clear water quickly becomes turbid, as in Experiment 39, showing 
that carbon dioxide is one 
of the products of animal 
respiration. 

51. Relation to Ani- 
mal Life. — Animals 
must have free oxygen 
in order to live ; plants 
give off oxygen in their 
process of breathing. 
Animals having lungs 
absorb the oxygen di- 
rectly from the air, 
while those having gills 
take up by this means 
the oxygen that the 

water has dissolved. The oxygen is taken through the 
lungs or gills into the red blood -corpuscles and carried by 
the blood to all parts of the body. In the minute capil- 
lary blood-vessels the oxygen and the constituents of the 
digested food unite, just as the fuel burns in the fire. The 
two processes differ chiefly in rapidity of combustion. In 
both cases the object is the same, to produce heat. The 
heat so produced by the burning of the food maintains 
the body's warmth. The chemical products are also the 
same, consisting mainly of water and carbon dioxide 
which are exhaled by the breath. Some of the tissues of 
animals are being continually burned up by oxygen. 
Unless the loss is made good by proper food, emaciation 
and death follow. If by any means the supply of oxygen 




60 AIR AND ITS CONSTITUENTS. 

is cut off, as by choking or drowning, this chemical tiction 
is arrested and the victim dies by suffocation. 

EXERCISES. 

1. Show that the terms addition and subtraction might be applied, 
to the processes involved in Experiment 53. 

2. Is phosphoric oxide soluble in water ? How did you ascertain 
the fact ? 

3. How can you ascertain whether the atmosphere of the school- 
room is contaminated with carbon dioxide or not? If you found that 
it was thus contaminated, what would you suppose to be the most 
probable source of the contamination? 

4. What is proved by the fact that the composition of our atmos- 
phere is variable ? • 

5. State the difference in the source of the supply of oxygen for 
living fishes and for animals that live on the land. 

6. Is it proper to speak of a molecule of air ? Why ? 

II. NITROGEN. 
Symbol, N ; density, 14 ; atomic weight, 14 ; valence, 1 to 5. 

52. Occurrence. — Nitrogen is widely diffused in nature. 
It is found free in some of the nebula? and in the earth's 
atmosphere. In combination, it exists in a number of 
minerals, as the sodium and potassium nitrates (niter) of 
Peru and India, and in ammonia and nitric acid in the 
atmosphere and natural waters. It also forms an essential 
part of most animal and vegetable substances. 

53. Preparation. — The usual way of preparing nitrogen 
is to burn out, with phosphorus, the oxygen from a portion 
of air confined over water, as shown in Experiment 53. 
Instead of the burning phosphorus, a jet of burning hydro- 
gen may be used. The nitrogen thus prepared is not 
perfectly pure, but nearly enough so for ordinary purposes. 



NITROGEN. 



61 



(«) Any method of getting the oxygen of the air to enter into com- 
bination and to form a compound that is easily removed from the 
residual nitrogen will answer. Thus, if a slow stream of air is passed 
over bright copper-turnings heated to redness in a glass tube, the 
oxygen will unite with the copper, leaving the nitrogen to be collected 
over water. 

(b) Pure nitrogen may be obtained by chemical processes, such as 

heating ammonium nitrite, which decomposes into water and nitrogen, 

as follows : 

(NH 4 )N0 2 + heat = 2H 2 + N 2 . 

54. Physical Properties. — Nitrogen is a transparent, 
colorless, tasteless, odorless gas. It is a little lighter 
than air or oxygen, and fourteen times as heavy as hydro- 
gen, a liter weighing 1.2544 grams. It is very slightly 
soluble in water. 

Relation to Combustion. 

Experiment 57. — Fill a bell-glass 
with oxygen, and a stoppered bell-glass 
of the same size with nitrogen. Cover 
their mouths with glass plates and 
bring them mouth to mouth. Remove 
the stopper and the glass plates and 
introduce a lighted taper having a long 
wick (or a pine splinter). As the taper 
passes through the nitrogen, the flame is 
extinguished; if the wick is still glowing, 
it will be rekindled in the oxygen. By 
moving the taper up and down from 
one gas to the other, it may be rekindled 
repeatedly before the gases become mixed 
by diffusion. 

55. Chemical Properties. — The leading characteristic of 
nitrogen is its inertness. Its properties are chiefly nega- 
tive. It enters into direct combination with but few 
elements. It is not easily burned nor is it a supporter of 




62 AIR AND ITS CONSTITUENTS. 

combustion. It may be burned to its oxide by passing an 
electric spark through a mixture of oxygen and nitrogen. 
It is not poisonous ; we are continually breathing large 
quantities of it, and it is an essential constituent of food. 
When breathed pure it kills by suffocation, by cutting off 
the necessary supply of oxygen, just as hydrogen or water 
does. Its compounds are generally unstable and energetic. 
Some of them are decomposed by being lightly brushed 
with a feather or by a heavy step on the floor. 

Note. — In the periodic system of the chemical elements (§ 148, b), 
nitrogen falls in Group 5, the other members of which are considered 
in Chapter XV. 

56. Uses. — The chief use of nitrogen is to dilute the 
oxygen of the air, and thus to prevent disastrous chemical 
activity, especially in the processes of respiration and 
combustion. 

57. Tests. — Nitrogen may be recognized by its physi- 
cal properties and its refusal to give any reaction with 
any known chemical test, except its combustion by the 
electric spark and the fact that it is absorbed by heated 
magnesium, to form a nitride of magnesium. 

58. Minor Constituents of Air. — Argon, helium, kryp- 
ton, neon, and xenon are constituents of the atmosphere 
existing only in small proportions, and distinguished by 
being chemically even more inert than nitrogen, which 
they so closely resemble in their properties that they were 
only recently discovered. As yet, no method has been 
found whereby they can be made to unite with any other 
element, and they are as yet unknown in combination. 
They were first separated from the air by burning the 



NITROGEN. 63 

nitrogen by the passage of an electric spark. The resi- 
due, consisting mainly of argon, was at first supposed to 
be a single element. However, through liquefying it by 
intense cold and high pressure, and fractionally distilling 
the liquid, these five elements have been isolated. They 
differ in their densities, boiling-points, and spectra. 

EXERCISES. 

1. What is meant by allotropism? Analysis? Synthesis? 

2. What is the difference between an elementary and a compound 
molecule ? 

3. Why does the burning of alcohol (C 2 H fi O) yield steam? 

4. Why does the gas-bottle become heated in the preparation of 
hydrogen ? 

5. Explain the statement that food is a fuel. 

6. Is hydrogen poisonous ? Can you live long in an atmosphere 
of hydrogen ? Why ? 

7. Is oxygen poisonous ? Can you live long in an atmosphere of 
oxygen ? Why ? 

8. Why is the word oxygen a misnomer ? 

9. Is the ordinary method of preparing oxygen analytic or 
synthetic ? 

10. What is the chief characteristic of oxygen? 

11. Why is the inner rather than the outer tube of the compound 
blowpipe used for oxygen ? 

12. Name five constituents of ordinary air. 

13. State three or more reasons for holding that the air is a 
mixture. 

14. What is the weight of 1 cu. m. of nitrogen ? Of oxygen ? 

15. State the composition of an explosive mixture of gases. 



CHAPTER IV. 

SOME NITROGEN COMPOUNDS. 

I. AMMONIA. 

59. Occurrence. — Ammonia (NH 3 ) exists in small quan- 
tities in the air, whence it is brought down to the earth 
by rain and dew. It is formed by the putrefaction of 
animal and vegetable matter. The ammonia of commerce 
is chiefly obtained from ammoniacal salts made in the 
purification of illuminating-gas, from the by-product of 
coke ovens, and from furnaces in which iron ore is smelted 
with bituminous coal. It was discovered long ago by 
distilling horn, and so was called hartshorn, a name that 
is still sometimes used. 



Preparation of Ammonia. 

Experiment 58. — In a mortar, or in the palm of the hand, rub to- 
gether equal weights of pulverized ammonium chloride (sal-ammoniac, 
NHjCl) and quicklime (CaO). Notice 
the smell before and after rubbing. 

2NH 4 C1 + CaO = CaCl 2 + 11,0 + 2XII,. 

Experiment 59. — Into a half-liter 
flask, pour about 200 cu. cm. of strong 
ammonia-water (ammonium hydroxide, 
NH 4 OII). Close the flask, n. with a <-<>rk 
carrying a funnel-tube and a delivery- 
tube. The delivery-tube should pass 
to the bottom of a tall drying-bottle, ?>. 
containing about a liter of quicklime 
broken into small pieces. Gently heat 
the liquid in a, and ammonia (which 
is a gas) will be given off* After pass- 

64 




Fig. 2& 



AMMONIA. 



65 



ing through b, it may be collected by upward displacement or over 
mercury. If collected over mercury, the funnel-tube in a must have 
a considerable length. 

Experiment 60. — Mix 25 or 30 grams of pulverized ammonium 
chloride with 50 to 60 grams of freshly slacked lime (CaO + H 2 = 
Ca0 2 H 2 ), that has been allowed to cool. Place the mixture in a half- 
liter flask and add enough water to cause it to aggregate in lumps 
when stirred with a rod. When the mixture is gently heated, am- 
monia is produced. 

2XH 4 C1 + Ca(OH) 2 = CaCL, + 2H 2 + 2NH 3 . 

The gas, after being dried, may be collected in bottles by upward 
displacement and the bottles corked. This is the most common way 
of preparing ammonia in the laboratory. 

Experiment 61. — From the flask of Experiment 60, pass the gas 
through a series of Woulffe bottles, partly filled with water. The 
delivery- tube of one bottle dips into the water in the next. A 




safety-tube, s (open at both ends), passes through the cork in the 
middle neck of each bottle. The delivery-tube of the generating flask 
should not dip into the water of the first bottle. This precaution 
prevents the possibility of water being forced back into the heated 
flask and breaking it. " It is well to keep the Woulffe bottles in ves- 
sels containing cold water, as heat is evolved in the condensation of 
the ammonia. At the end of the experiment, put the ammonia- water 
just prepared into convenient bottles, cork the bottles tightly, and 
save the liquid for future use. See Appendix, § 7. 

SCHOOL CHEMISTRY 5 



66 



NITROGEN COMPOUNDS. 



60. Preparation. — Anhydrous ammonia is made from 
gas-house liquor and other sources by distillation, and by 
cooling and compressing the distillate until it liquefies. 
For aqua ammonia (ammonia-water), which is a solution 
of the gas in water, the distilled gas is absorbed in cold 
water ; by heating this solution the gas may be recovered. 
Ammonia may be made by heating an ammoniacal salt, 
like ammonium chloride, with a strong base, like lime, or 
by absorbing free nitrogen by red-hot metallic magne- 
sium and treating the resulting nitride of magnesium 
with water. 

Physical Properties of Ammonia. 

Experiment 62. — Fill a liter bottle, a, with ammonia 
by upward displacement. By holding at the mouth of 
the inverted bottle a moistened strip of turmeric-paper 
or of red litmus-paper, the experimenter will be able to 
tell when the bottle is filled; the turmeric will turn 
brown or the litmus blue. Close the bottle with a cork 
(a rubber stopper is preferable), through which passes 
a small glass tube. Place the end of this tube in water 
colored with red litmus solution. The water will, in a 
moment, rush into the bottle with violence, changing 
from red to blue as it enters. 




61. Physical Properties. — Ammonia is a colorless, irres- 
pirable gas, and has a pungent odor. It is much lighter 
than air, only eight and a half times as heavy as hydrogen. 
It liquefies under a pressure of six and a half atmospheres 
at 10°, four and a half atmospheres at 0°, or one atmos- 
phere at - 40°. The liquid solidifies at - 85°. Under 
ordinary conditions, the liquid rapidly evaporates, produc- 
ing intense cold. This forms the basis of Carre's refrigera- 
tion process and of ice manufacture. 




AMMONIA. 67 

Chemical Properties of Ammonia. 

Experiment 63. — From the drying-bottle of Experiment 59, lead the 
delivery-tube, d, through a narrow glass cylinder to its upper end. 
As the ammonia issues at a, try to light it ; it will refuse 
to burn. Through the flexible tube, b, pass a current o£ 
oxygen into the cylinder. The jet of ammonia, being 
now surrounded by an atmosphere of oxygen, may be 
lighted ; it will burn with a yellowish flame. 

2NH 3 + 30 2 = 6H 2 + N 2 . 

Experiment 64. — Pass a stream of oxygen from the 
gas-holder through a strong aqueous solution of ammonia 
in a flask. Heat the flask, and bring a flame into con- 
tact with the mixed gases as they issue from the neck of 
the flask. They will burn with a large yellow flame. Fig. 31. 

Experiment 65. — Upon a piece of broadcloth or of dark-colored 
calico, let fall a few drops o£ dilute sulphuric acid. The acid will 
produce red spots. Apply ammonia-water to the spots and they will 
disappear. This is a familiar experiment in most laboratories. 

62. Chemical Properties. — Ammonia and its water solu- 
tion have strong alkaline properties, neutralizing acids and 
restoring vegetable colors changed by acids. The gas is 
combustible only when mixed with oxygen, this reaction 
burning only the hydrogen and setting free the nitrogen. 
Ammonia has a strong attraction for water and is remarkably 
soluble in it. One volume of water absorbs 803 volumes of 
the gas at 14°, or 1146 volumes at 0°, the gas entering into 
chemical combination with water as follows : 

NH 3 + H 2 = NH 4 OH. 
This saturated solution (aqua ammonia fortior) has a den- 
sity of .85, and contains about thirty -five per cent of 
the gas. A weaker solution (aqua ammonia, ammonia- 
water), containing ten per cent or less of the gas, is more 
commonly sold. 



68 



NITKOGEN COMPOUNDS. 



(«) When ammonia is dissolved in water, the reaction liberates a 
large quantity of heat (see § 145) ; of course, a like quantity of heat 
is absorbed when the gas is prepared from its solution as described in 
the preceding paragraph. 

(/;) As will be explained in a later paragraph, the atomic group, 
NH 4 , is called ammonium. The product of the reaction above written, 
NH 4 OH, is sometimes called ammonium hydroxide, just as though 
the ammonium had united directly with hydroxyl. Ammonia unites 
additively with acids (for example, hydrochloric acid, HC1) thus : 

NH 3 + 1IC1 = NH 3 HC1. 

The effect is the same as if an ammonium group, NH 4 , had replaced 
.the hydrogen of the acid, and the formula for the product is so 
written, NH 4 C1. (See Experiment 58.) The name of the product, 
ammonium chloride, as well as the formula, suggests that the ammo- 
nium group may thus replace a single atom of hydrogen in an acid. 
This suggestion is given more color by the fact that when the hydrox- 
ide and the acid react, the equation is 

NH 4 OH + HC1 = NH 4 C1 + H 2 0. 

In similar manner, ammonium nitrate (XH 4 X0 3 ) is formed from 
nitric acid (HX0 3 ). 

63. Volumetric Composition. — When ammonia gas is 
decomposed, its volume is doubled, two volumes of the 
compound yielding four volumes of its elementary constit- 
uents. Of these, three volumes are hydrogen and one 
volume is nitrogen. In other words, the compound yields 
one and a half times its volume of hydrogen, and half its 
volume of nitrogen. Of course, there is no change in 
weight, the constituents consisting of three parts of 
hydrogen to fourteen parts of nitrogen. This may be 
represented to the eye as follows : 



H 

l 



H 

1 



+ 



1 



+ ' 



N 
14 



HN: 5 

17 



AMMONIA. 69 

(a) Suppose 100 cu. cm. of ammonia to be confined over mercury 
in an eudiometer. By producing electric sparks in it, the gas is decom- 
posed, and increases its volume to 200 cu. cm. Add, say 100 cu. cm. 
of oxygen, and produce a spark in the mixed gases. There is a shrink- 
age of 225 cu. cm., the gases now measuring 75 cu. cm. The shrinkage 
was due, of course, to the formation of water. Hence-, two-thirds of 
the 225 cu. cm., or 150 cu. cm., was hydrogen, and the other 75 cu. 
cm. was oxygen. But, as we introduced 100 cu. cm. of oxygen, and 
only 75 cu. cm. of it has combined, the other 25 cu. cm. must be in 
the eudiometer as part of the residual 75 cu. cm. Consequently, we 
have left 50 cu. cm. of nitrogen, and 25 cu. cm. of oxygen. The 50 
cu. cm. of nitrogen and the 150 cu. cm. of hydrogen came from the 
100 cu. cm. of ammonia. 

64. Uses. — Ammonia-water is used in the laboratory 
for many purposes, in the household for softening "hard" 
water and for cleansing purposes, and in many industrial 
processes. It is largely used in the preparation of sodium 
carbonate, in the production of aniline colors, and in the 
manufacture of indigo. Liquid ammonia is used in the 
freezing of artificial ice. The salts of ammonia are largely 
used as constituents of commercial fertilizers, this being 
the principal use of ammonia. 

65. Tests. — The tests for ammonia are its pungent 
odor, its turning moistened red litmus-paper blue, and the 
fumes of the ammonium chloride it produces with hydro- 
chloric acid as in Experiment 9. Ammonia may be set 
free from its compounds by heating them with potassium 
hydroxide, and then detected as above indicated. 

EXERCISES. 

1. (a) What weight of hydrogen is contained in 17 grams of 
NH 3 ? (b) What volume of hydrogen? 

2. (a) What volume of hydrogen can be produced by the decom- 
position of 2 liters of NH 3 ? (b) What weight of hydrogen ? 



70 



NITROGEN COMPOUNDS. 



3. (a) What weight of hydrogen can be united with 28 grams of 
nitrogen to form ammonia? (b) What volume of hydrogen? 

4. (a) What weight of nitrogen can be united with 9 grams of 
hydrogen to form NH 3 ? (b) What will be the weight of the product? 

5. (a) If 100 cu. cm. of ammonia are decomposed in an eudiom- 
eter, 100 cu. cm. of oxygen added, and an electric spark passed 
through the mixed gases, what gases will remain? (b) What will be 
the volume of each ? 

6. Why were the safety tubes used in Experiment 61 ? 

7. What is the difference between ammonia-water and liquid 
ammonia? State one use of each. 

8. Explain the formation of boiler-scale. 

9. State two uses of free hydroxyl. 

10. Describe an experiment for showing approximately the volu- 
metric composition of atmospheric air. 

11. Describe the electrolysis of water. Make a sketch of the 
apparatus used in the process. 

12. What is the lightest gas that you have studied ? The heaviest? 



II. NITROGEN OXIDES. 

66. Nitrogen Oxides. — Nitrogen combines with oxygen 

in five different ratios to form 
five different chemical compounds 
or oxides. 

Preparation of Laughing-gas. 

Experiment 66. — Into a small Florence 
flask place a tablespoonf ul of ammonium 
nitrate. Heat gently and carefully over 
the sand-bath or a piece of wire gauze, 
and collect the gas over warm water. 
Remove the delivery-tube from the 
water before the gas stops flowing. 

67. Nitrogen Monoxide. — Nitrogen monoxide (nitrogen 
protoxide, nitrous oxide, laughing-gas, N 2 0) is prepared 
by decomposing ammonium nitrate by heat. 

NH 4 N0 3 + heat = N 2 + 2H,G. 




NITROGEN OXIDES. 



71 



(a) To show that water is produced, interpose between the Florence 
flask and the water-pan, a condensing bottle placed in iced water, as 
shown at c in Fig. 32. Test the liquid that collects in this bottle by 
dropping a small piece of potassium into it. The flask would break 
before all of the XH 4 X0 3 was decomposed, but by heating a small 
quantity of the nitrate upon platinum foil, it will be seen that no resi- 
due is left. When needed in large quantities, the gas under pressure 
in steel cylinders may be bought of dealers in dental supplies. 

Properties of Laughing-gas. 

Experiment 67. — Repeat Experiments 31, 34, and 35, using N" 2 
instead of oxygen. (These are simply combustions in oxygen, the 
binary gas being decomposed into its elements.) 

68. Properties. — Nitrogen monoxide is a colorless, sweet- 
tasting gas, and a good supporter of combustion. When 
a substance is burned in the monoxide, free nitrogen is 
formed. At the temperature of ignition, the oxygen is 
more strongly attracted by the combustible substance 
than is the nitrogen with which it was united. When 
pure nitrogen monoxide is mixed with one-fourth its vol- 
ume of oxygen, it may be safely inhaled, producing the 
effects that have secured for it the name of laughing-gas. 
If its inhalation is continued, it acts as an anaesthetic. 
It should not be thus inhaled except under the direction 
of a competent medical attendant. 

69. Volumetric Composition. — The composition of nitro- 
gen monoxide is strictly analogous to that of steam, two 
volumes of nitrogen uniting with one of oxygen to form 
two of this compound. 



N 
14 


+ 


N 
14 


+ 


O 

16 



N20 

44 



72 NITROGEN COMPOUNDS. 

When decomposed by electric sparks, it yields one and a 
half times its own volume of mixed gases, as represented 
by the typical squares. 

Nitric Oxide. 

Experiment 68. — Partly till the gas-bottle with small lumps of 

ferrous sulphate (blue vitriol, copperas) and pour in enough water 

to seal the funuel-tube. Add strong nitric acid in small quantities. 

Collect the gas over water, rejecting as impure the part first collected. 

70. Nitric Oxide. — Nitric oxide (nitrosyl, NO) may be 

prepared as in the preceding experiment, or by the action 

of dilute nitric acid upon copper clippings, turnings, or 

filings. The apparatus is arranged as shown in Fig. 7. 

The generating bottle is, at first, filled with red fumes 

(§ 74) but the gas collected over water is colorless. In 

this reaction the nitric acid (HN0 3 ) gives up a part of 

its oxygen to the copper to form copper oxide, nitric 

oxide, and water. 

3Cu + 2HNO a = 3CuO + 2NO + H 2 0. 

The copper oxide thus formed unites with some of the 

excess of acid used to form copper nitrate, the solution 

of which gives the blue color noticed. 

CuO + 2HN0 3 = Cu(N0 3 ) 2 + H 2 0. 

These changes actually occur in one reaction which may 

be written thus : 

3Cu + 8HN0 3 = 2NO + 3Cu(N0 3 ) 2 + 4H 2 0. 

The blue solution of copper nitrate should be properly 

labeled and saved for future use. 

(a) As we shall soon see, nitric acid is composed of nitrogen pen- 
toxide (N 2 5 ) and water. Similarly, one of the proximate constituents 
of ferrous sulphate is ferrous oxide (FeO). In the preparation of 
nitric oxide as already indicated, the copper of the ferrous sulphate 



XITKOGEN OXIDES. 



73 



reduces the X 2 5 to XO. In thus taking oxygen from the pentoxide 
the copper is oxidized to CuO, and the FeO is changed to a higher 
oxide of iron, namely ferric oxide (Fe 2 Oo). 

Properties of Nitric Oxide. 

Note. — In the next three experiments, keep (as far as possible) 
the nitric oxide from contact with the air. 

Experiment 6g. — Into a bottle of XO, lower a burning splinter, a 
burning candle, or sulphur burning in a deflagration-spoon (see Ap- 
pendix, § 18) . It will not burn in the gas. 

Experiment 70. — Into a bottle of XO, 
lower a deflagration-spoon containing a 
bit of vigorously burning phosphorus, the 
size of a pea. It will continue to burn 
with great brilliancy. 

Experiment 71. — In a jar of XO, place 
a few drops of carbon disulphide. Close 
the bottle for a few minutes to allow the 
liquid to evaporate and its vapor to mix 
with the oxide. In a dark room, bring 
a lighted taper to the open mouth of the 
jar. The mixture burns with a vivid light 
rich in actinic rays. F IG . 33. 

71. Properties. — The leading property of this colorless 
gas is its strong attraction for oxygen. Its relation to 
combustion is peculiar. Ordinary combustibles will not 
burn in it at all ; phosphorus may be melted in the gas 
without kindling, but when well aflame it burns in it 
with great energy. The gas is only slightly soluble in 
water, but dissolves readily in a solution of ferrous sul- 
phate. It may be condensed to a colorless liquid. The 
experiments already given show that, while the oxygen 
of nitric oxide is held so loosely that it may be extracted 
from the nitrogen by certain substances, it is held more 
firmly than is the oxygen of nitrous oxide. 




74 



NITROGEN COMPOUNDS. 



72. Volumetric Composition. — This is the first compound 
that we have studied, the gaseous constituents of which 
unite without condensation. One volume of oxygen unites 
with one volume of nitrogen to form two volumes of nitric 
oxide. 



N 
14 


+ 


O 
16 



NO 

30 



73. Nitrogen Trioxide. — This is a dark-blue, unstable 
liquid, sometimes called nitrous anhydride (N 2 3 ). It 
begins to decompose at a temperature of —21° below zero, 
and at a temperature of 3.5° it rapidly separates into 
nitrogen monoxide and nitric oxide. For this reason, 
it does not exist in the gaseous state. It unites with cold 
water to form nitrous acid. 

N 2 3 + H 2 = 2HN0 2 . 

(a) Xitrogen trioxide is sometimes called nitrogen sesquioxide 
because the number of its oxygen atoms is one and a half times the 
number of its nitrogen atoms, the Latin prefix, sesqui, signifying one 
and a half. 

Nitrogen Peroxide. 

Experiment 72. — Into a jar of nitrosyl, 
standing over water, pass a stream of oxygen 
from the gas-holder. After the red fumes 
that are promptly formed have been dissolved 
by the water, repeat the experiment several 
times, noticing the phenomena carefully. 
Ascertain the nature of the solution by testing 
it with litmus-paper. 

Experiment 73. — Fill a large bell-glass with 
nitric oxide at the water-bath. Cover the 
mouth under water with a glass plate, invert 
the bell-glass and remove the plate. The 
nitric oxide absorbs oxygen from the air and 
Fig. 34. forms a cloud of the now familiar red fumes. 




NITROGEN OXIDES. 



75 



74. Nitrogen Peroxide. — Nitrogen peroxide (nitryl, 
N0 2 ) is the brownish red gas that is best prepared by 
bringing together two volumes of nitric oxide and one 
volume of oxygen, both constituents being perfectly dry. 
It is an energetic oxidizing agent. It may be liquefied and 
solidified. In the presence of water it forms acid com- 
pounds, probably a mixture of nitric and nitrous acids. 

(a) In the solid and liquid conditions, this oxide seems to have the 
formula N 2 4 , whence the name sometimes used, nitrogen tetroxide. 
In other words, the solid and the liquid oxide are polymeric with the 
dark-colored gas. See § 252 (a) . 

75. Volumetric Composition. — The composition of nitro- 
gen peroxide may be represented as follows : 



N 
14 


+ 


o 

16 


+ 


o 

16 



N02 

46 



(a) If we modify Experiment 72 by adding one volume of pure 
oxygen to two volumes of pure nitric oxide in a graduated tube over 
mercury, we may notice that the three volumes of gas are condensed 
into two volumes of nitrogen peroxide. 



NO 


+ 


NO 



= 2N02 



76. Nitrogen Pentoxide. — Nitrogen pentoxide (nitric 
anhydride, N 2 5 ) is a crystalline white compound, so un- 
stable that it spontaneously decomposes in a sealed tube 
into oxygen and nitrogen peroxide. It is particularly 
interesting on account of its relation to nitric acid. 

N 2 5 + H 2 = 2HN0 3 . 

Note. — For definitions of hypothesis, theory, and law, see Avery's 
School Physics, § 10. 



76 



NITROGEN COMPOUNDS. 



77. Law of Definite Proportions. — The truth stated in 
§ 9 has been verified by numberless analyses and may 
be formulated as follows : Any given chemical compound 
always contains the same elements in the same relative 
quantities. 

(a) Identity of properties implies identity of composition, but we 
shall find that identity of composition does not necessarily carry with 
it identity of properties. 

78. Law of Multiple Proportions. — If two substances 
combine to form more than one compound, and the quan- 
tity of one constituent is kept constant, the varying quan- 
tities of the other constituent are in the ratio of small 
wJiole numbers. 

(a) This important principle was discovered in 1808 by John 
Dalton. To account for it he proposed the atomic theory (§ 1-Y2). 
It is best illustrated by the nitrogen oxides just studied. 







By Gua 


VIMETRIC 


By Vol 


l' METRIC 






A XA 






Analym>. 




Actual. 


Ratio. 


Actual. 


Ratio. 




. 


. 


• 




= ^ 


B 














:c ■ 


J^AMES. 


2 


i l a 


to 


to 




= to 
























X 


7. Z 


fe C 




aa 


ft C 


£ 


C 
















z a 


c 






3 - 




















a - 






















r -r 


•r 




3 B 


-H B. 






~: | 


£ 


£ 


> > 


> > 


Nitrogen monoxide 


N„0 


28 : 16 


If 


1 


2 : 1 


2 : 1 


Nitric oxide 


NO 


14 : 10 


If 


o 


1 : 1 


2 : 2 


Nitrogen trioxide 


N 2 3 


28:48 


If 


3 


2 : 3 


2 : 3 


Nitrogen peroxide 


NO, 


14 : 32 


i ; ; 


4 


1 :2 


2:4 


Nitrogen pentoxide 


n 2 o s 


28 : 80 


if 


5 


2 : 5 


2 :5 



Attention is called to the consecutive numbers 1, 2, 3, 4, and 5, in 
the columns headed " Ratio." 



NITROGEN ACIDS, ETC. 77 

(/;) This law necessarily results from the definition of an atom 
(§ 4). Since the atoms can not be divided, the elements can com- 
bine only atom by atom and, consequently, either in the ratio of their 
atomic weights or some simple multiple of that ratio. 

EXERCISES. 

1. Is the air a mixture or a compound ? Why? 

2. State the points of resemblance and difference between oxygen 
and nitrogen. 

3. (a) Is the process of preparing oxygen analytic or synthetic? 
(b) Of preparing X0 2 ? (c) N 2 0? 

4. How could you prove the presence of ox} T gen in air? 

5. If two liters of nitrogen and one of oxygen are combined, what 
will be the name and volume of the product ? 

6. (a) How is ammonia-water prepared? (b) How is liquid 
ammonia prepared? (c) What will result from the decomposition 
of a liter of laughing-gas into its constituent elements? (d) Write 
the reaction for the preparation of ammonia. 

7. When nitrous oxide is mixed with hydrogen and the mixture 
exploded, nitrogen and a compound vapor are formed. Write the 
reaction. 

8. Xame the products formed by the decomposition of ammonium 
nitrate by heat. 

0. One cubic centimeter of ice-cold water will absorb more than 
a liter of one of the gases that you have studied. How may you pre- 
pare and test that gas without any laboratory apparatus ? 

10. How would you guard against personal injury in the cutting 
and handling of phosphorus? 

1-1. Give the reason for the caution in the Xote preceding Experi- 
ment 69. 

12. Determine experimentally the action of nitric oxide and of 
nitrogen peroxide upon blue litmus-paper. 

III. NITROGEN ACIDS, ETC. 

79. Nitric Acid. — The most important of the nitrogen 
acids is nitric acid (aqua fortis, HN0 3 ). Its chief sources 
are potassium nitrate (saltpeter or niter) which is ob- 



78 



NITROGEN COMPOUNDS. 



tained in abundance in India, and sodium nitrate (Chile 
saltpeter or soda niter), which is found as an efflorescence 
on the soil of a sterile region in Chile and Peru, and 
exported in large quantities from those countries. At 
present, it is made almost exclusively from Chile saltpeter. 

Preparation of Nitric Acid. 
Experiment 74. — Into a quarter-liter retort, a, having a glass stop- 
per, put 50 grams of pulverized potassium nitrate (KN0 3 ), or 40 grams 
of pulverized sodium nitrate (N"aN0 3 ), and 35 cu. cm. of strong sul- 
phuric acid (H 2 S0 4 ). The materials should be introduced through 
the tubulure, s, and care taken that none falls into the neck of the 
retort. It is well to use a paper funnel for the nitrate and a funnel- 
tube for the acid. Replace the stopper and place the retort upon sand 
in a shallow sheet-iron or pressed-tin pan, supported by a ring of the 
retort-stand over the lamp, or upon wire gauze, as shown in the figure. 
The use of the sand-bath or the gauze lessens the danger of breaking 

the retort. Place the neck 
of the retort loosely in the 
mouth of a Florence flask, 
r, or other convenient re- 
ceiver, kept cool by water. 
It is well to cover the re- 
ceiver with cloth or bibu- 
lous paper; the w T ater may 
be brought by a rubber 
} tube siphon from a pail of 
water sufficiently elevated. 
As the retort is heated, the 
nitrate liquefies, reddish 
fumes appear, and HN0 3 condenses in the neck of the retort and in 
the receiver. The fumes in the retort will soon disappear ; continue 
the distillation until they reappear. 

KN0 3 + H 2 S0 4 = KHS0 4 + HN0 3 . 
Transfer the acid to a glass stoppered bottle and save it for future 
use. After the retort has become thoroughly cool, the solid residue, 
potassium-hydrogen sulphate, should be dissolved by heating with 
water and then removed. 




Fig. 35. 



NITROGEN ACIDS, ETC. 79 

80. Preparation. — Nitric acid may be made by the 
combination of nitrogen pentoxide and water, bnt it is 
generally prepared from a nitrate by distillation with 
sulphuric acid (H 2 S0 4 ). 

(a) In the arts, the retort is made of cast-iron and the distillate 
is condensed in earthenware receivers. A higher temperature and 
frequently only half as much H 2 S0 4 are used. 

2KX0 3 + H 2 S0 4 = K,S0 4 + 2HX0 3 , 
2XaX0 3 + H 2 S0 4 = Xa 2 S0 4 + 2HX0 3 . 

81. Physical Properties. — Nitric acid is a faming 
liquid, colorless when nearly pure, but generally slightly 
tinted with the fumes seen in the retort during its prepa- 
ration. It has a density of 1.52, freezes at — 47°, and 
boils with partial decomposition at 86°. On standing, it 
decomposes slowly, with formation of nitrogen peroxide, 
which dissolves in the acid and gives it a brownish 
color. It may be mixed with water in all proportions, 
the aqua fortis of commerce usually containing sixty-eight 
per cent of nitric acid. 

Chemical Properties of Nitric Acid. 

Experiment 75. — Pulverize and heat a few grams of charcoal. 
Upon the heated charcoal, pour a little strong HX0 3 . The charcoal 
will be rapidly oxidized to combustion. 

Experiment 76. — From the end of a meter-stick drop a thin slice 
of phosphorus into strong HX0 3 . The phosphorus will be oxidized 
with violent combustion. 

Experiment 77. — Into dilute HX0 3 dip a skein of white sewing- 
silk. In a few minutes, remove the silk and wash it thoroughly with 
water. The silk will be permanently colored yellow. 



80 NITROGEN COMPOUNDS. 

Experiment 78. — Get a sheet of " Dutch leaf " from a sign painter ; 
put it into a test-tube, and pour upon it a small quantity of IIX0 3 . 
The metal will be instantly dissolved. 

Experiment 79. — Cover a smooth piece of brass or of copper with 
a film of beeswax. With a sharp instrument, write your name upon 
the metal, being sure to cut through the wax. Cover the writing 
with strong HN"0 3 . In a few moments the name will appear in a 
tracery of minute bubbles. A few moments later, wash the acid 
away with water, and remove the wax. The autograph will be 
etched upon the metal. 

Experiment 80. — Into a test-tube, put a brass pin and cover it with 
HNOg. Red fumes will appear, and the liquid will be colored blue 
by the copper nitrate formed. Brass is an alloy that contains copper. 

82. Chemical Properties. — Nitric acid is a powerful 
oxidizing agent, and one of the most corrosive known 
substances. It colors nitrogenous animal substances 
(e.g., silk, skin, and parchment) yellow, and converts 
many non-nitrogenous substances (e.g., cotton and glyce- 
rin) into violently explosive compounds. It dissolves 
all of the common metals, except gold and platinum, 
forming nitrates. Its oxidizing power is due to the 
ease with which it is decomposed, giving up part of its 
oxygen and forming nitrogen oxides, that contain a 
smaller proportion of oxygen. 

83. Uses. — Nitric acid is largely used in the laboratory 
and in the arts, in the manufacture of guncotton, nitro- 
glycerin, etc., and in the preparation of aqua regia 
(§ 119). Engravers use it for etching on copper and 
steel. Nitric acid or nitrates constitute the foundation 
of almost all high explosives. 

(a) Gunpowder is made by mixing potassium nitrate with sulphur 
and charcoal. When it is ignited, the oxygen of the niter combines 



NITROGEN ACIDS, ETC. 81 

with the sulphur and charcoal, producing instantly large volumes of 
gases. 

(b) Guncotton, largely used for filling torpedoes and as a basis for 
making blasting gelatine, is made by immersing purified cotton in a 
mixture of strong nitric and sulphuric acids. After a proper length 
of time, the cotton is carefully washed to free it from every trace of 
acid and dried. The product burns quietly when ignited but explodes 
violently by concussion. 

(c) Nitroglycerin, the most important of modern explosives, 
is made by slovvly running a small stream of glycerin into a mixture 
of strong nitric and sulphuric acids, keeping the mixture cool. The 
product, an oily liquid, is carefully washed free from acid, since the 
smallest quantity left may cause it to heat and explode. Like gun- 
cotton, nitroglycerin may be burned quietly by ignition, but is 
exploded by shock. In the pure state it is unsafe to transport. 

(//) Dynamite is made by mixing nitroglycerin with enough of 
some inert substance like wood-pulp or soft earth to give it the con- 
sistency of a solid. While it may be exploded by detonation, it is 
less susceptible to the small shocks incident to transportation. 

(e) Guncotton and nitroglycerin are incorporated with each other 
by mixing with a mutual solvent, to produce the various kinds of 
blasting gelatin, and smokeless powder. 

Tests for Nitric Acid. 

Experiment 81. — Into a narrow test-tube place about 1 cu. cm. of 
concentrated sulphuric acid. Incline the test-tube and upon the acid 
pour carefully, so that they do not mix, a like quantity of a strong 
solution of ferrous sulphate (green vitriol) to which has been added 
a single drop of dilute nitric acid. A brown ring will form at the line 
of contact of the tw^o liquids. This ring is due to the formation of a 
brown compound of the ferrous sulphate w T ith the nitrogen peroxide 
set free from the HXO s , and is one of the most delicate tests for the 
presence of a nitrate. 

Experiment 82. — Into a test-tube put a few cubic centimeters of 
a dilute solution of indigo. Add HNOo until the blue solution is 
bleached. The acid oxidizes the blue indigo to a colorless compound. 

84. Tests. — In testing for nitric acid, first try bine 
litmus-paper. If this test-paper is not reddened when 

SCHOOL CHEMISTRV 6 



82 NITROGEN COMPOUNDS. 

clipped into the liquid in question, the liquid is not ah 
acid. If it is reddened, the liquid is an acid. As the 
nitrates are all easily soluble, tests for nitric acid yield no 
precipitates. Free nitric acid may be detected by its 
bleaching an indigo solution, or by its forming red fumes 
when added to copper bits or filings. Nitrates show the 
same effects when heated with sulphuric acid, because of 
the nitric acid thus set free. The nitrates also deflagrate 
when thrown upon burning charcoal. 

Nitrates. 

Experiment 83. — In a small evaporating dish (see Appendix, § 20), 
place a few cubic centimeters of HX0 3 and add an equal bulk of 
water. In another vessel, place a small quantity of diluted ammonia- 
water. Into the first liquid, dip a strip of blue litmus-paper. The 
change of color shows an acid. Dip this litmus-paper (now red) into 
the other liquid. The restoration of the blue color shows the presence 
of an alkali. To the first liquid add the second, in small quantities 
at first, and finally drop by drop. Stir the mixture continually with 
a glass rod, and test with blue litmus-paper after each addition of 
ammonia-water. At last, it will be found that the mixture will 
neither redden blue litmus-paper nor restore red litmus-paper to its 
original blue. It has neither an acid nor an alkaline reaction. The 
acid has been " neutralized " by the alkali, and we have a solution of 
a neutral salt. Without boiling the liquid, evaporate it until, when 
the glass rod is removed, the adhering liquid becomes almost solid 
upon cooling. Crystals will now form upon the cooling of the liquid ; 
these crystals are to be carefully drained and dried. They are ammo- 
nium nitrate (NH 4 N"0 3 ). 

85. Nitrates. — Compounds formed by replacing the 
hydrogen of nitric acid by ammonium (NH 4 ) or by a 
metal are called nitrates. They have neither an acid nor 
an alkaline reaction; that is, they produce no change in 
vegetable colors, such as litmus. In nature, they are pro- 



NITROGEN ACIDS, ETC. 83 

duced by the decay of the nitrogen -containing com- 
pounds of animal and vegetable tissues — the final product 
of their oxidation. This decay and oxidation are caused 
by the growth of nitrifying bacteria. The nitrates are 
among the most important plant foods, and are largely 
used as components of commercial fertilizers. 

(«) Nitrates are also produced in the soil from the free nitrogen 
of the air by the action of certain bacterial organisms that grow 
most freely around the roots of leguminous plants, such as peas, 
clover, and vetch. The cultivation of these crops, therefore, increases 
the nitrate contents of the soil, and makes it more fertile for the 
growth of other crops that require much nitrogen. Plants are unable 
to assimilate directly the free nitrogen of the air. Many ways have 
been attempted to convert atmospheric nitrogen into nitrogen com- 
pounds of economic value, but none of them have yet been commer- 
cially successful. 

(b) The fact that air and nitrifying bacteria rapidly convert 
animal and vegetable substances into nitrates and carbon dioxide 
is utilized in the disposal of the sewage of cities by the systems of 
intermittent or aerated filtration. The sewage is spread on large 
sand-filters at the proper temperature for the growth of the nitrifying 
bacteria, and given free access of air. Under these conditions, the 
water is rapidly purified and fitted for return to the natural water 
courses. 

86. Nitrous Acid. — Nitrous acid (HN0 2 ) does not exist 
free. When a nitrite is decomposed by a strong acid, a 
mixture of nitrogen oxides, instead of nitrous acid, is 
produced. The nitrite may be prepared by reducing a 
nitrate. Thus, if 20 or 30 grams of potassium nitrate 
are melted and thoroughly stirred with about twice that 
quantity of metallic lead, the nitrate will be reduced to 
potassium nitrite. 

KN0 3 + Pb = KN0 9 + PbO. 



84 NITROGEN COMPOUNDS. 

When a solution of this nitrite is decomposed by an acid, 
analogy would suggest such a reaction as the following : 

2KN0 2 + H 2 S0 4 = K 2 S0 4 + 2HN0 2 . 

As a matter of fact, instead of nitrous acid, the substance 
formed is nitrogen trioxide, which is nitrous acid less the 
elements of water. 

2HN0 2 = N 2 3 + H 2 0. 

The oxide is so unstable that it quickly breaks up, forming 
other nitrogen oxides. The phenomenon may be attrib- 
uted to the fact that the attraction of. hydrogen for 
oxj'gen is greater than the forces that tend toward the 
equilibrium of the nitrous acid molecule. 

(a) Many compounds that contain oxygen and hydrogen show 
this tendency to decompose with the formation of water. This is 
what would naturally take place when the attraction between the 
oxygen and the hydrogen atoms is greater than the forces that are 
at work in the molecule to keep its constituents in equilibrium. 
Many compounds that do not thus break up at ordinary temperatures 
do so when heated. (See § 07). As we shall soon see, nitrogen tri- 
oxide is one of a class of compounds called anhydrides. 

87. Hyponitrous Acid. — This acid (HXO) does not 
exist in the free state, but the corresponding salt, potas- 
sium hyponitrite (KNO), is known. We may imagine 
this reaction: ^q + H 2 = 2HN0. 

EXERCISES. 

1. Describe the laboratory preparation of nitric acid. 

2. Is nitric acid a stable compound or is it easily decomposed? 
Illustrate. 

3. How would you etch your name on the blade of a hand-saw? 

4. What is the difference between nitroglycerin and dynamite ? 



NITROGEN ACIDS, ETC. 85 

5. "What is the most common test for an acid ? 

6. I have a liquid that reddens blue litmus-paper, and that gives 
off reddish-brown fumes when I drop a few copper cartridge-shells 
into it. Write the molecular formula for the acid. 

7. In what way do certain bacteria contribute to plant life? 

8. Show that nitrogen trioxide is a dehydrated acid. 

9. Name three physical and two chemical properties of oxygen. 

10. («) If 180 cu. cm. of ammonia are decomposed by electric 
sparks, what will be the volume of eacli of the resultant gases? 
(b) If, then, 130 cu. cm. of oxygen are introduced and another 
electric spark is produced in the containing vessel, the temperature 
being 16°, what will be the volume of the remaining gaseous contents 
of the vessel? 

11. (a) If a mixture of 50 cu. cm. of hydrogen and 50 cu. cm. of 
oxygen is exploded in an eudiometer, what will be the name and 
volume of the remaining gas? (b) "What precaution must be taken 
in measuring the gases ? 

12. Explain why. in Experiment 26, it is safe to remove the towel 
from the bottle after the gas has been ignited. 



CHAPTER V. 
ACIDS, BASES, AND SALTS. 

88. Three Important Groups. — The last chapter intro- 
duced to us a member of each of three large and important 
classes of chemical compounds. Nitric acid represents a 
group having certain properties in common and called 
acids ; ammonia represents another group called bases ; 
the union of an acid and a base, as shown in Experiment 
83, produces a member of a third group called salts. 

89. Acids. — All acids contain hydrogen ; the rule does 
not work both ways. The hydrogen of an acid is easily 
replaceable by a metal. This property distinguishes acids 
from all other chemical substances. 

(a) Another property of most acids is a sour taste. Any substance 
that has a sour taste is an acid or contains an acid as one of its con- 
stituents. Thus lemons and oranges contain citric acid, apples and 
many other fruits contain malic acid, and vinegar owes its sour taste 
to acetic acid. 

(b) Xext to the taste, the simplest test for an acid is its action 
upon vegetable colors. Nearly all acids change litmus from blue to 
red and produce analogous changes in many other vegetable colors. 
Any substance that reddens blue litmus is an acid or contains an acid. 

90. Bases. — Substances of this class have the common 
property of uniting with an acid in such a way as to 
destroy its typically acid properties. A part of the base 
replaces the hydrogen of the acid and thus forms a coin- 
pound that is not sour and does not change litmus or other 



ACIDS, BASES, AND SALTS. 87 

vegetable colors. All bases contain oxygen ; many of 
them also contain hydrogen, an atom of each being united 
to form a group of hydroxyl (OH); there is always an- 
other constituent, generally a metal. For example, lime 
(CaO) and sodium hydroxide (NaOH) are bases. 

(«) Aii alkali is a base that is soluble in water, combines with fats 
to form soaps, has a caustic action on animal and vegetable tissue, 
turns reddened litmus back to blue, and changes turmeric from yel- 
low to brown. The most common alkalis are the hydroxides (§ 9(j) 
of sodium, potassium, calcium, and ammonium. As distinguished 
from the fixed alkalis, ammonia is called the volatile alkali. 

(b) When the base and the acid are brought into sufficiently inti- 
mate contact, as when a solution of one is mixed with a solution of 
the other, the hydrogen atoms in the acid molecules combine with the 
hydroxyl of the basic molecules to form water. The remaining atoms 
or the radicals with which the acid hydrogen and the basic hydroxyl 
were united, also unite to form a compound called a salt. As in most 
bases the hydroxyl is united with an atom of a metal, most salts con- 
tain a metallic element. To this general rule ammonia and ammo- 
nium salts are exceptions, the group of atoms XH 4 (i.e., the radical 
ammonium) acting the part of a metallic atom. 

(c) Acids and bases, then, have each the power of destroying the 
properties that are typical of the other. This process is called neu- 
tralizing ; the two bodies are said to neutralize each other ; when the 
resulting product has no power to change the color of either blue or 
red litmus, it is said to be neutral. 

Salts. 

Experiment 84. — Dissolve 5 grams of caustic soda (sodium hy- 
droxide, sodium hydrate, iSTaOH) in 50 cu. cm. of water. Slowly 
add dilute hydrochloric acid (HC1), frequently testing the solution 
with blue litmus-paper until a final drop turns the paper slightly red. 
If too much acid has been added by mistake, make the solution again 
alkaline with the soda, and repeat the neutralization with the acid 
until the test-paper is only very faintly reddened. Then evaporate 
the solution on a water-bath until the residue is dry. Taste the 
resulting solid and determine its reaction with litmus. 



88 ACIDS, BASES, AND SALTS. 

91. Salts. — In the above experiment, the caustic soda, 
an alkaline base, reacted with the hydrochloric acid as 
follows: Na0 H + HC1 = NaCl + II 2 0. 

The hydrogen and the sodium changed places. The product 
of such a reaction between an acid and a base, in which 
one or more of the hydrogen atoms of the acid have been 
replaced by metallic atoms or basic radicals, or in which 
the hydrogen atoms of the base are more or less replaced 
by non-metallic atoms or acid radicals, is called a salt, 
(a) A salt may be formed — 

(1) By replacing one or more of the hydrogen atoms of an acid 
with electropositive (metallic) atoms or radicals. Compare HX0 3 
and KXOo. 

(2) By replacing one or more of the hydrogen atoms of a base with 
electronegative (non-metallic) atoms or compound radicals. Compare 
KOH and K(X0 2 )0 or KXO,. 

(3) By the direct union of an anhydride (see § 95) and a basic 
oxide. Thus, calcium sulphate results from the direct union of sul- 
phuric anhydride and calcium oxide (quicklime): S0 3 +CaO = CaS0 4 . 

Xote. — Of these three views of the formation of a salt, the first 
is the one most frequently taken, but occasionally the other two 
are convenient. An acid is sometimes called a "hydrogen salt"; 
e.g., hydrogen nitrate (HX0 3 ). 

92. Classification of Salts. — Salts may be normal (or 
neutral), double, acid, or basic. 

(a) A normal salt is one that contains neither basic nor acid hydro- 
gen (see § 94). All of the basic hydrogen of the acid, or acid hydro- 
gen of the base from which it was formed has been replaced as stated 
in the last paragraph. K 2 S0 4 and CuS0 4 are normal salts. 

(b) A double salt is one in which hydrogen of the acid from which 
it was formed has been replaced by metallic (or positive) atoms of 
different kinds. For example, common alum, A1 2 K 2 (S0 4 ) 4 , is a 
double salt. 

(c) An acid or hydrogen salt is one that contains basic hydrogen 
(see § 91). As only part of the replaceable hydrogen of the acid has 



ACIDS, BASES, AND SALTS. 89 

been replaced, the salt, in most cases, still acts like an acid, reddening- 
bine litmus. The potassium-hydrogen sulphate, KHS0 4 , mentioned 
in Experiment 74, is an acid or hydrogen salt. 

(d) A basic salt is one that contains acid hydrogen. Only part of 
the hydrogen of the base from which it was formed has been replaced, 
on account of which, in many cases, it still acts like a base, turning- 
reddened litmus to blue. For example, lead hydroxide is a base with 
the symbol, PbH 2 2 or H 2 PbO.>. Replacing half of this hydrogen 
with the acid radical, NO a , we have H(X0 2 )Pb0 2 , the symbol for 
lead hydronitrate, a basic salt. 

(e) A binary acid will yield a binary salt when its hydrogen is 
replaced. Thus, HC1 yields NaCl. 

93. The Nomenclature of Acids. — Acids take their 
names from their non-metallic radicals, such as chlorine 
and sulphur (see § 15). A few acids contain no oxygen. 
The names of these begin with the prefix hydro-, and 
end with the suhix -ic, as hydrochloric acid (HC1), the 
most important of this class. If only two ternary acids 
of a non-metallic element are known, the one in which 
the molecule contains the greater number of oxygen atoms 
takes the termination -ic ; the other takes the termination 
-ous. Sometimes the radical forms three or even four 
ternary acids. The acid in which the molecule contains 
a number of oxygen atoms greater than that of the -ic 
acid takes the prefix per-; the one in which the number 
is less than that of the -ous acid takes the prefix, hypo-. 
The use of these prefixes and suffixes will be made clear 
by a study of the following examples : 



HC10 4 .... perchloric acid 

HC10 3 chloric acid 

HC10 2 .... chlorous acid 

HCIO . . . kypochloTous acid 



H 2 S0 4 .... sulphuric acid 
H 2 S0 3 .... sulphurous acid . 
H 2 S0 2 . . %/>osulplmrous acid 



This system of nomenclature was introduced by Lavoisier. 



90 ACIDS, BASES, AND SALTS. 

94. Basicity of Acids. — The hydrogen of an acid that 
may be readily replaced by a metal is called basic hydro- 
gen. If the acid molecule has one atom of basic hydrogen, 
the acid is called a monobasic acid. If it has two such 
atoms, the acid is called a dibasic or bibasic acid ; if three, 
it is tribasic ; if four, it is tetrabasic. 

(a) The basicity of an acid molecule depends upon the number of 
its directly exchangeable hydrogen atoms and may generally be repre- 
sented by the number of hydroxyl groups it contains. For example : 

HN0 3 is a monobasic acid (OH) — (N*0 2 )'. 

H 2 S0 4 is a dibasic acid fOH)/ (S ° 2 )''* 

(0H) X 

H 3 P0 4 is a tribasic acid (OH)-(PO)'". 

(OH)/ 

Be it remembered, however, that the basicity of an acid molecule 
depends, not upon the total number of its hydrogen atoms, but upon 
the number of them that may be directly exchanged for metallic 
atoms. H 3 P0 4 is called tribasic, not because it has three hydrogen 
atoms, but because it may form three distinct salts with one metal. 

95. Anhydrides. — An oxide of a non-metallic (or elec- 
tronegative) element which, with the elements of water, 
may form an acid, is called an anhydride. Nitrogen 
trioxide and nitrogen pentoxide, and sulphurous and 
sulphuric oxides are anhydrides. They unite directly 
with water to form the corresponding acids, thus : 

N 2 3 + H 2 = 2HN0 2 (nitron* acid), 
N 2 5 + H 2 = 2HN0 3 (nitric acid), 

50 2 + H 2 = H 2 SG 3 (sulphurous acid), 

50 3 + H 2 = H 2 S0 4 (sulphunV acid). 



ACIDS, BASES, AND SALTS. 91 

96. Nomenclature of Bases. — The bases that contain 
hydrogen are often called hydroxides or hydrates, distin- 
guished by the names of the metals that they severally con- 
tain, as sodium hydroxide (NaOH), potassium hydroxide 
(KOH), and calcium hydroxide [Ca(OH) 2 ]. They may 
be regarded as hydroxyl compounds, or as water in which 
half of the hydrogen has been replaced by a metal. Many 
of them may be made by simply bringing the metal into 
contact with water, as, when sodium is thrown upon 
water, hydrogen is evolved from the water, and sodium 
hydroxide (sodium hydrate or caustic soda) is formed, 

thus ; Na 2 + 2H 2 = 2NaOH + H 2 . 

97. Nomenclature of Salts. — The names of the salts of 
any acid are derived from the name of that acid and quali- 
fied by the name of the metallic atoms that they contain, 
as explained in § 15. Thus we have 

Sodium hypochlorite (NaCIO) from hypochlorous acid. 
Sodium chlorite (NaC10 2 ) from chlorous acid, 
Potassium chlorate (KC10 3 ) from chloric acid. 
Potassium perchlorate (KC10 4 ) from perchloric acid. 

The names of the salts derived from binary acids, like 
hydrochloric acid (HC1), are exceptions. Following the 
general rule of binary compounds, they end in -ide, like 
sodium chloride (NaCl). 

EXERCISES. 

1. (a) What is the difference between an atom and a molecule? 
(b) Between a physical and a chemical property? (c) Define and 
illustrate base, acid, salt, (d) State the differences between an -ic, 
an -ous, and an -ale compound. 



92 ACIDS, BASES, AND SALTS. 

2. (a) Why is sulphurous acid said to be dibasic? (/>) "What is 
the difference between an acid sulphite and a normal sulphite? 
(c) Between an acid sulphite and a hydrogen sulphite? 

3. Is every alkali a base? Is every base an alkali? 

4. AVhy are there no acid nitrates? 

'). Xame the acid and the base, the reaction of which yields the 
salt with which you are the most familiar. 

IS. What is the common name of hydroxyl hydride? 

7. "Write the molecular formulas for hydrochloric and hypo- 
chlorous acids. 

8. When mercuric oxide (HgO) is heated, it decomposes. Write 
the reaction. (Owing to the high price of mercuric oxide, this re- 
action is seldom employed.) 

9. State the composition of water, both volumetric and gravimetric. 
10. What word describes the hydrogen in an acid salt? In a 

basic salt? 



CHAPTER VI. 

VALENCE, RATIONAL SYMBOLS, RADICALS. 

98. Valence. — The valence of an element is its relative 
combining capacity measured by that of hydrogen as the 
unit ; in other words, it indicates the number of hydrogen 
atoms with which an atom of the element can unite, or 
the number of hydrogen atoms that it can replace. Thus, 

In hydrochloric acid (HC1), the valence of chlorine is 1. 

In water (H 2 0), the valence of oxjgen is 2. 

In ammonia (H 3 N), the valence of nitrogen is 3. 

In marsh-gas (H 4 C), the valence of carbon is 4. 

Similarly, one atom of potassium (K) can replace one 
atom of hydrogen in a molecule of nitric acid (HN0 3 ) 
yielding a molecule of potassium nitrate (KN0 3 ), while 
one atom of calcium (Ca) can replace two atoms of hydro- 
gen in a molecule of sulphuric acid (H. 2 S0 4 ) yielding a 
molecule of calcium sulphate (CaS0 4 ). One atom of potas- 
sium can replace one atom of hydrogen, but no more, its 
valence is one ; one atom of calcium can replace two atoms 
of hydrogen, but no less, its valence is two. 

(a) Atoms are classified according to their valence as monads, 
dyads, triads, tetrads, pentads, hexads, and heptads, from the Greek 
numerals. They are similarly described by the adjectives univalent. 
bivalent, trivalent, quadrivalent, quinquivalent, sexivalent, and septiv- 
alent, from the Latin numerals. Thus, oxygen is a dyad, or it is 
bivalent ; carbon is a tetrad, or it is quadrivalent. 
93 



94 VALENCE, RATIONAL SYMBOLS, RADICALS. 

(b) The valence of some elements varies with the natures of the 
elements with which they are brought into contact. Thus, -with 
hydrogen alone, a nitrogen atom can combine with only three atoms 
forming a molecule of ammonia (NH 3 ). In this case, nitrogen acts 
as a triad. But when ammonia is brought into contact with hydro- 
chloric acid (HC1), the nitrogen atom unites with both the hydrogen 
and the chlorine to form ammonium chloride (XH 4 C1). In this case, 
nitrogen acts as a pentad. When atoms of a given element thus act 
with different valences, they frequently form compounds as dissimilar 
as atoms of different kinds would do. A change in the valence of an 
atom implies a change in all its chemical relations. K,0 is as differ- 
ent from X 2 5 as H 2 is. 

(c) The valence of an atom is indicated by Roman numerals placed 
above, or minute marks placed above and at the right of the symbol, 

IV 

as C or N'". They should not be confounded with the figures below 
and at the right of the symbol. 

(d) Sometimes the words " quantivalence,'* " equivalence," and 
even " atomicity " are used in the sense in which we have used the 
word valence. The word " atomicity " more properly refers to the 
number of atoms in a molecule. 

99. Graphic Symbols of Atoms. — The graphic symbol 
of an atom represents its valence by lines or bonds 
extending from the symbol, as follows : 

Monad, Dyad, Triad, Telrad, Pentad, Hexad. 

H- 0= Ns C= =Ps ssSs 
The number of bonds is significant ; their direction is 

not. Thus, the graphic symbol of an atom of oxygen 

i 
may be written — O— , 0=, 0—, — O, 0<, etc. 

100. Graphic Symbols of Molecules. — The graphic sym- 
bol or formula of a molecule is composed of the graphic 
symbols of the constituent atoms. It attempts to indi- 
cate the constitution of the molecule, not by showing the 
arrangement of the atoms in space, for we know nothing 
about that, but by showing that certain atoms are united 



VALENCE, RATIONAL SYMBOLS, RADICALS. 95 

to certain other atoms. Sometimes these symbols suggest 
the possible modes of formation and of decomposition of 
substances ; sometimes they are necessary to enable us to 
distinguish between substances that have the same per- 
centage composition and different properties (see § 252). 

(«) The graphic symbol of H 9 may be written H — O — H ; that of 
H O 

I V II 

H 3 1S T ,H-X-H; that of C0 2 ,0 = C = 0; that of HN0 3 , H - O - N = O ; 

VI 

and that of S0 9 , O = S = 0. It will be noticed that each atom has the 

II 
number of bonds that represents its valence. A modification of the 
graphic symbol, often called the semigraphic symbol, is sometimes 

X N0 2 
conveniently used, as (HO) — (HO), or Ca<^ 

\N0 2 
(b) Less important than the graphic formula, and yet often con- 
venient, is the typical formula, examples of which are here given : 



Free Hydrogen. Water. Ammonia. Harsh-gas. 

H I 



SI Si" «, 



H fC- 



101. Radicals. — An atom or group of atoms that seems 
to determine the character of a molecule is called a radi- 
cal. Such an atom is called a simple radical ; such a 
group of atoms is called a compound radical. In the 
graphic symbols given above, it will be noticed that, in 
each case but one (S0 2 ), every atom has its valence fully 
satisfied; i.e., each bond of each atom is engaged. Such 
atomic groups are said to be saturated. But the group, 

O = S = O, has two free bonds. 

ii 
Such an unsaturated group of atoms, assumed to exist in a 

compound body and to remain intact in many of the chemical 



96 VALENCE, RATIONAL SYMBOLS, RADICALS. 

changes that the body under' joes, is called a compound radi- 
cal. It may enter into combination like a simple atom, 
always acting with a valence equal to the number of unsatis- 
fied bonds. See §94 (a). 

(a) The names of compound radicals generally terminate in -yl, as 
nitrosyl (NO) and nitryl (N0 2 ). Two of these atomic groups may 
unite, like two atoms, to form a saturated molecule. If, from II-O-H, 
we remove one atom of H, we have the compound radical H-0-, 
called hydroxyl. Two of these univalent groups may unite to form 
H 2 2 , as follows : (HO)-(HO) or H-O-O-H. 

EXERCISES. 

1. Considering chlorine to be a monad, write tin? graphic symbols 
for CLO, C1 2 3 , HCIO and HC10 3 . H-O-Cl = O ? 

2. What valence for chlorine is indicated by II 

O 

3. Write three graphic symbols for S0 2 , two of which shall repre- 
sent it as a compound radical (sulphuryl) and all of which shall rep- 
resent sulphur as a dyad. 

4. Write two graphic symbols for SO.,, one of them representing 
sulphur as a dyad, the other representing sulphur as a hexad. 

5. Name the substances symbolized as follows, indicating the 
symbols for compound radicals : 

N = N = X X 

\/ ; -N = 0; -0-X = 0; >0; 

O o = x/ 

X X H-0-X = 

State the difference between the indications given by the last two 
symbols. 

6. (a) Write the molecular formula for the hydroxide of the 
monad radical, nitryl. (b) For the hydroxide of (SO.,)". 

7. Why may not hydrogen dioxide be represented by II-O-II-O? 

8. Write the graphic or structural formula for ammonia. 

9. Considered as a compound radical, what is the valence of 
ammonium? 

10. Write the full graphic formula for ammonium hydroxide. 



CHAPTER VII. 

THE HALOGEN GROUP. 

I. CHLORINE. 

Symbol, CI. ; density, 35.2 ; atomic weight 85.2 ; valence, 1, 3, 4, 5, 7. 

102. Occurrence. — Chlorine does not occur free in 
nature, but it is very abundant and widely diffused, 
being a constituent of common salt (sodium chloride, 
NaCl), and of potassium 
chloride (KC1). Sea- 
water may be made to 
yield about five times its 
volume of chlorine. The 
name comes from the 
Greek chloros, meaning 
green. 



Preparation of Chlorine. 

Experiment 85. — Into a 
flask of about 300 cu. cm. 
capacity put about 30 grams 
of dry sodium chlorine (com- 
mon salt, NaCl), and add an 
equal weight 'of coarse man- 
ganese dioxide (Mn(X) and 
35. cu. cm. of strong sulphuric 
acid (H 2 S0 4 ), previously di- 
luted with an equal bulk of 
water. The stopper of the 

SCHOOL CHEMISTRY — 7 97 




98 THE HALOGEN GROUP. 

flask should carry a delivery-tube, passing to the bottom of a tall, dry 
glass cylinder, and a safety-tube. Shake the flask to mix the materials, 
place it upon a sand-bath, and heat gently. Chlorine is evolved and 
is collected in the cylinder by downward displacement. When the 
cylinder is full, close the mouth with a greased glass plate. The 
yellowish green color of the gas enables the experimenter to see when 
the cylinder is full. Be careful not to inhale the gas. Perform all 
experiments with chlorine in a draught of air or in a ventilating closet. 

2XaCl + Mn0 2 + 3H 2 SO, = MnS0 4 + 2HXaS0 4 + 2H 2 + Cl 2 . 

When sulphuric acid a£is on sodium chloride alone, hydrochloric 
acid and sodium sulphate are formed. 

H 2 S0 4 + 2XaCl = 2HC1 + Na 2 S0 4 . 

But when the manganese dioxide is present, some of its oxygen unites 
with hydrogen from this hydrochloric acid, forming water and setting 
chlorine free, as indicated above. 

Experiment 86. — In apparatus arranged as described in Experiment 
85, gently heat 12 grams of manganese dioxide and 25 cu. cm. of 
hydrochloric acid. 

Mn0 2 + 4HC1 = MnCl 2 + 2H 2 + Cl 2 . 

The gas may be collected, although with loss, over hot water or 
strong brine. It may be noticed that in Experiment 85, as truly as 
here, the method of preparing the gas is to oxidize the hydrogen 
of the hydrochloric acid to water, thus liberating the chlorine of the 
acid. 

Experiment 87. — Put a small bottle containing 15 or 20 grams of 
bleaching-powder into a glass vessel of several liters capacity. Then, 
by means of a funnel-tube passing through the pasteboard cover of 
the large jar, pour dilute sulphuric acid upon the bleaching-powder. 
Chlorine will be evolved and displace the air from the jar. 

103. Preparation. — Chlorine is generally prepared in- 
directly from common salt. The immediate chemical 
process is by oxidizing the hydrogen of hydrochloric acid, 
thus setting free the chlorine. Different agents, generally 



CHL0K1NE. 99 

potassium chlorate or manganese dioxide, are used in 
such oxidation. 

KClOg + 6HC1 = KC1 4- 3H 2 + 3CI 2 . 

Chlorine is prepared on the commercial scale as an ac- 
companiment of the Leblanc process for making sodium 
carbonate. 

Physical Properties of Chlorine. 

Experiment 88. — Prepare some chlorine-water by passing a current 
of chlorine through water, in a series of Woulffe bottles, arranged as 
in Experiment 61, except that the tubes should not dip so deep into 
the water. The chlorine-water may be preserved for a considerable time 
by placing it in bottles wrapped in opaque 
paper and closed with greased stoppers. 

Experiment 89. — Into a wide-mouthed 
bottle filled with chlorine, pour water until 
the jar is a third full of the liquid. Close the 
mouth of the bottle with the hand and shake 
the bottle. The gas will be absorbed, a 
vacuum formed, and the bottle held against 
the hand by atmospheric pressure. FlG - 37 « 

104. Physical Properties. — Chlorine is a yellowish 
green, irrespirable gas with a suffocating odor and 
astringent taste. Even a very small quantity of it in 
the air produces violent coughing and irritation of the air 
passages when it is inhaled. It may be easily liquefied 
by pressure or cold. If it was not so corrosive, it could 
be transported and handled commercially in the liquid 
form. At very low temperatures, it crystallizes to a 
yellow mass that melts at — 102°. It is largely soluble in 
water, one volume of which, at 10°, dissolves two and a 
half volumes of the gas. The solution has most of the 
properties of the gas, and, when saturated, gives off the 

to* a 




100 



THE HALOGEN GROUP. 



gas freely on exposure to the air. One volume of charcoal 
will absorb two hundred volumes of the gas. Chlorine 
gas is nearly two and a half times as heavy as air. 

Chemical Properties of Chlorine. 

Experiment 90. — Fill a tall bottle or cylinder holding 500 cu. cm. 
or more with chlorine. The gas may well be dried by passing it over 
calcium chloride, as in Experiment 28, or by passing it over fragments 
of pumice saturated with sulphuric acid (H 2 S0 4 ), or by allowing the 
gas to bubble through sulphuric acid. Slowly sift freshly prepared 
filings of metallic antimony into the bottle. The two elements will 
combine with the evolution of heat and light. Filings of metallic 
arsenic or bismuth give similar effects. 

Experiment 91. — Place a thin slice of dry phosphorus in a defla- 
gration-spoon and place it in a jar of chlorine. The gas and the solid 
combine directly with 
a pale flame. 

Experiment 92. — 
Burn a jet of hydrogen 
or one of illuminating 
gas, in an atmosphere 
of chlorine. Reverse 
the conditions and 
burn a jet of chlorine 
in hydrogen (see Fig. 
23). Try to burn a 
jet of chlorine in oxy- 
gen, and a jet of oxy- 
gen in chlorine. 

Experiment 93. — 
Pour chlorine-water 
into a solution of 
hydrogen sulphide 
(H 2 S, see Experiment 
260). The chlorine 
robs the sulphide of 
its hydrogen to form hydrochloric acid, while the sulphur is pre- 
cipitated. 




CHLORINE. 



101 



Experiment 94. — In a darkened room, mix equal volumes of 
hydrogen and chlorine, previously prepared in the light. With the 
mixture, fill three stoat soda bottles. Wrap one of the bottles with 
a towel, remove the eork and apply a'flame to the mouth of the bottle. 
The mixed gases combine with an explosion. The towel will protect 
the experimenter if the explosion breaks the bottle. Wrap the 
second bottle with a towel to which a string, several meters long, has 
been attached. Carry the covered bottle into a sunny place and, by 
means of the string, remove the towel. The suu's direct rays cause 
the mixed gases to explode. This experiment succeeds best with a 
thin glass bulb filled with a gaseous mixture obtained by the electroly- 
sis of hydrochloric acid. Place the third bottle in diffused sunlight. 
The two gases will unite gradually and quietly. Allow the bottle to 
remain for future use. 

Experiment 95. — Fill five wide-mouthed bottles with dry chlorine 

and close their mouths with greased glass plates. 

Heat some oil of turpentine over the water-bath. 
Fasten a tuft of shredded tissue- 
paper or of cotton to a wire or 
splinter, dip it into the hot turpen- 
tine, and quickly plunge it into the 
first bottle of chlorine. The paper 
or cotton will generally take fire 
and burn with a very dense smoke 
(Fig. 39). Into the second bottle, 
thrust a burning dry wood splinter ; 
into the third, thrust a burning 
piece of paper; into the fourth, a 
burning wax or tallow taper (Fig. 40) ; into the fifth, a 
deflagration-spoon containing burning petroleum. Note 

the effect in each case. 

Xote. — The combustibles used in the last experiment contain 

hydrogen and carbon. This hydrogen combines with the chlorine 

and sets the carbon free, as smoke. 

Experiment 96. — Fill a tall tube with chlorine and invert it over a 
cup of water. Place the tube in a sunny place. After a few days, 
test the gaseous contents of the tube for oxygen, and the water for an 
acid. Seek for the odor of chlorine. 

H o + CL = 2HC1 + O. 





Fig. 10. 



102 THE HALOGEN GROUP. 

105. Chemical Properties. — Chlorine is a very energetic 
chemical agent. It unites directly with all of the common 
elements except oxygen, nitrogen, and carbon, its attrac- 
tion for hydrogen being very remarkable. 

Bleaching. 

Experiment 97. — Pass a current of dry chlorine through a bulb- or 
a U-tube containing a bit of dry calico print. After a few moments, 
attach a second tube containing a bit of similar calico that has been 
moistened. Notice that the chlorine passes the dry calico without 
bleaching it, but that it quickly bleaches the moist calico with which 
it subsequently comes into contact. 

Note. — Pink or blue paper-cambric is desirable for the above ex- 
periment. The presence of moisture is necessary to this bleaching 
action. Dry chlorine seldom acts directly on coloring matters, but 
oxygen in its "nascent state," or at the instant of its liberation from 
water, does so act. In this case, the nascent oxygen is the immediate 
bleaching agent. 

Experiment 98. — Nearly fill seven test-tubes with chlorine-water. 
Into the first, pour a few drops of indigo solution; into the second, 
litmus solution ; into the third, cochineal solution ; into the fourth 
and fifth, aniline dyes of different colors ; into the sixth, the colored 
petal of a flower, and into the seventh put a strip of colored calico or 
of paper-cambric. The colors will quickly disappear. 

Experiment 99. — Dip a piece of colored cambric or of calico into 
a half liter of water into which 15 grams of bleaching-powder have 
been stirred. Notice the effect upon the color of the cloth. Then dip 
the cloth into very dilute hydrochloric or sulphuric acid. Notice the 
effect on the color of the cloth. Wash the cloth thoroughly in 
water. 

106. Bleaching-powder. — For convenience in transpor- 
tation, chlorine is absorbed, at the works where it is manu- 
factured, in slightly moistened slacked lime with which it 
unites chemically, forming calcium hypochlorite (CaCl 2 2 ) 
and calcium chloride (CaCl 2 ). From this bleaching- 



CHLORINE. 103 

powder, chlorine is easily set free by adding enough acid 
to combine with the calcium present. The quantity of 
bleaching-powder made each year is very large and in- 
creasing. Its principal use is as a bleaching agent in the 
manufacture of paper and of cotton goods, and for recov- 
ering gold from certain of its ores. It is sometimes called 
chloride of lime* 

(a) The chlorine required in the manufacture of bleaching-powder 
is made by three different processes : 

1. The oldest method (now the least used) is that of treating 
manganese dioxide with hydrochloric acid. 

2. Another method is by the electrolysis of some chloride, gener- 
ally common salt. The electric current breaks up the sodium chloride 
into sodium and chlorine. The sodium thus freed unites with water, 
producing hydrogen and sodium hydroxide (caustic soda, NaOH). 
Thus caustic soda is an important product of this process. 

3. The method, known from the name of the inventor as the 
Deacon process, is the one most largely used. It consists in passing 
air and hydrochloric acid together through a heated chamber contain- 
ing clay balls saturated with copper sulphate. Under these conditions, 
the hydrogen of the acid and the oxygen of the air unite and leave 
the chlorine free. 

4HC1 + 2 = 2H 2 + 2C1 2 . 

Uses of Chlorine. 

Experiment ioo. — Upon a piece of printed paper, write your name 
in ink. Dip the paper into chlorine-water. The written characters 
will be bleached out ; the printed characters will remain. 

Experiment ioi. — Repeat Experiment 93, noticing the odor of 
hydrogen sulphide before the addition of the chlorine-water and its 
absence after such addition. 

107. Uses. — Chlorine is used in the arts as a bleaching 
and disinfecting agent, its action depending very largely 
upon its attraction for hydrogen. The non-mineral color- 



104 THE HALOGEN GROUP. 

ing matters are largely composed of oxygen, hydrogen, 
nitrogen, and carbon. When such coloring matter is 
brought into contact with chlorine in the presence of 
moisture, the chlorine attacks the hydrogen of both, the 
nascent oxygen thus liberated from the water greatly 
aiding the chlorine in the decomposition of the coloring 
substance. Colorless compounds are formed by a process 
of chlorination and oxidation. Chlorine has little effect 
upon mineral colors, or free carbon. 

Tests for Chlorine. 

Experiment 102. — Prepare a quantity of thin starch paste by 
boiling 30 cu. cm. of water and stirring into it half a gram of starch 
previously reduced to the consistency of cream by thoroughly mixing 
with a few drops of cold water. In this paste, dissolve a piece of 
potassium iodide, half the size of a pea. Into a test-tube, put 10 cu. cm. 
of water and five or six drops of this mixture of starch and potassium 
iodide. Shake the tube vigorously for a few seconds and let a few 
drops of chlorine-water fall into it. Notice the blue color thus formed. 
The chlorine decomposes the potassium iodide ; the free iodine colors 
the starch. 

Experiment 103. — Into the solution of starch and potassium iodide, 
dip two or three strips of white paper. Hold one of these strips of 
test-paper in a current of chlorine. The white paper is turned to blue. 
Remove the stopper from the bottle containing chloride of lime 
(bleaching-powder) and hold another strip of the test-paper in the 
atmosphere of chlorine that fills the upper part of the bottle. The 
paper is instantly colored blue. 

Experiment 104. — Place a strip of gold-leaf in saturated chlorine- 
water. The gold will be dissolved. 

108. Tests. — Free chlorine is easily distinguished by 
its odor ; pure chlorine, by its color. Chlorine is also 
easily detected by its bleaching action upon organic color- 
ing matters, or by its forming a blue color with a mixture 



HYDROCHLORIC ACID. 105 

of starch and potassium iodide. This last-mentioned re- 
action is very delicate, but an excess of chlorine removes 
the color and the same effect is produced b.y bromine, ozone, 
and a few other actively oxidizing substances. A cloud of 
ammonium chloride is formed when chlorine comes into 
contact with ammonia, and this serves as a delicate test for 
its presence when hydrochloric acid is known to be absent. 

EXERCISES. 

1. When chlorine-water is exposed to sunlight, HC1 is formed and 
oxygen is set free, (a) Write the reaction. (Jj) What volume of 
chlorine is necessary thus to set free 20 cu. cm. of oxygen ? 

2. Chlorine unites with the metals acting as a monad, {a) Sym- 
bolize the binary compounds of chlorine with the following: Xa'; K' ; 
Cu"; Au'" ; Ag' ; Fe" ; Zn" ; (Fe.,) v . (b) Symbolize the nitrates 
formed by replacing the hydrogen in nitric acid by the several metals 
just mentioned. 

3. About how many liters of chlorine may be obtained from 10 
liters of sea-water ? 

4. May chlorine be collected by upward or by downward displace- 
ment? Why? 

5. Which is the more largely soluble in water, chlorine or 
ammonia ? 

6. With which does chlorine combine the more readily, oxygen or 
hydrogen ? Give a reason for your answer. 

7. With which does chlorine combine the more readily, hydrogen 
or carbon ? Describe an experiment that supports your answer. 

8. In what proportions do chlorine and nitrogen unite? 

9. Of what is the valence of an element a numerical expression? 
10. What is the difference between a molecule of Lake Superior 

copper and a molecule of Montana copper ? 

II. HYDROCHLORIC ACID. 

109. Source. — Hydrochloric acid (hydrogen chloride, 
HC1) is the only known compound of hydrogen and chlo- 
rine. In its preparation, the hydrogen is generally fnr- 



106 



THE HALOGEN GROUP. 



nished by sulphuric acid (H 2 S0 4 ), and the chlorine by 

common salt (sodium chloride, NaCl), the cheapest and 

most abundant source of chlorine. The pure acid is a gas, 

the water solution of which constitutes the muriatic acid 

of commerce. 

(a) Hydrochloric acid is found in the exhalations of active vol- 
canoes, especially Vesuvius and Hecla, and in the waters of several 
South American rivers that have their rise in volcanic regions. 

110. Preparation. — Hydrochloric acid is almost always 
prepared from common salt by distillation with sulphuric 
acid. 

(a) Into a liter Florence flask, put 30 grams of NaCl and 30 cu. cm. 
of concentrated sulphuric acid. Heat the flask gently over the sand- 
bath and collect the gas by 
downward displacement in 
dry jars, as in the preparation 
of chlorine. By holding a 
piece of moistened blue 
litmus-paper at the mouth of 
the jar, the experimenter can 
easily tell when the jar is full. 

NaCl + H 2 S0 4 

= HC1 + XaHS0 4 . 

(b) At a higher tempera- 
ture, the same quantity of 
sulphuric acid would combine 
with twice as much sodium 
chloride, yield twice as much 
hydrochloric acid, and leave 
sodium sulphate (Xa 2 *0 4 ) 
instead of sodium-hydrogen 
sulphate (XaHS0 4 ). 

2XaCl + H 2 S0 4 

= 2HC1 + Xa 2 S0 4 . 




HYDEOCHLOKIC ACID. 



107 



The greater heat necessary for this latter reaction would be severe 
upon the apparatus. At the end of the experiment, the NaHS0 4 
remaining in the flask may be easily removed with warm water. 

(c) Hydrochloric acid may be prepared by the direct union of equal 
volumes of its constituents. See Experiment 91. 

(d) In the arts, the retort used is an iron cylinder, or the retort is 
replaced by a brick furnace. Sometimes an improved "salt-cake" 
furnace is used. This consists of two chambers, a kind of mufl&e, G, 
in which the first reaction takes place, and a reverberatory, E, in 
which may be secured the higher temperature needed for the second 
reaction. The two chambers may be separated by closing the con- 
necting aperture. The gaseous acid from either chamber may be led 




Fig. 42. 

off separately and dissolved in water contained in a series of earthen- 
ware "Woulffe bottles. Very large quantities (thousands of tons weekly) 
of the acid liquid are made as an incidental product of the manufac- 
ture of sodium carbonate. 

(e) Diy, gaseous HC1 may be obtained by heating the acid liquid 
and passing the gas given off through a drying-tube or bottle. 



Physical Properties of Hydrochloric Acid. 

Experiment 105. — Fill a long test-tube with dry hydrochloric acid 
and invert it over mercury. Thrust a bit of ice into the mouth of the 



108 



THE HALOGEN GROUP. 



tube 




Fig. 43. 



The ice and gas will quickly disappear, the mercury rising in 
the tube. Explain. 

Experiment 106. — Fill a bottle with 
"dry HC1. Close the bottle with a cork 
carrying a glass tube and invert it over 
water colored with blue litmus. The 
water will soon enter the bottle with 
violence, and its color will be changed 
from blue to red (see Fig. 30). 

Experiment 107. — Pass HC1 from the 
generating flask through a series of 
Woulffe bottles arranged as in Experi- 
ment 61, except that the delivery-tube 
from each bottle should barely dip into 
the water of the next bottle. It is well 
to place the Woulffe bottles in water to 
keep them cool. When the gas ceases to flow, test the contents of 
each bottle with blue litmus-paper. Bottle the liquid and save it for 
future use. 

111. Physical Properties. — Hydrochloric acid is a color- 
less gas having an acid taste and pungent odor. It is 
irrespirable, corrosive, and neither combustible nor a sup- 
porter of combustion. It is a little heavier than air, its 
density being 18.25. It liquefies at ordinary tempera- 
tures under a pressure of eighty-six atmospheres. This 
liquid has a density of 1.27, boils at -80°, and freezes 
at -115.7° to a white, crystalline mass. The gas is 
remarkably soluble in water, one volume of which, at the 
ordinary temperature, absorbs about 450 volumes of the 
gas, or 505 volumes at zero. This saturated solution, 
the muriatic acid of commerce, fumes strongly in the air 
because of the strong attraction of the gaseous acid for 
the moisture of the air. It has a density of 1.21 and 
readily gives up the acid gas when heated. If pure, it 



HYDROCHLORIC ACID. 109 

freezes at temperatures below — 40° to a butter-like mass 
having the composition HC1 + 2H 2 0. The commercial 
acid is yellow from dissolved impurities. 

Chemical Properties of Hydrochloric Acid. 

Experiment 108. — Nearly fill a test-tube with dilute, commercial 
HC1 and drop into it a few pieces of granulated zinc. The zinc is 
quickly dissolved. What gas escapes ? Write the reaction. Repeat 
the experiment with as many other metals as you can readily obtain. 

Experiment 109. — Tn a beaker, place several pieces of marble (cal- 
cium carbonate, CaCO s ), and pour upon them some HC1 solution. 
Write the reaction. Repeat the experiment, using lime (CaO) 
instead of marble. 

112. Chemical Properties. — Hydrochloric acid acts upon 
many metals and their oxides, forming chlorides, most of 
which are soluble in water. 

(a) The liquefied anhydrous HC1 does not act upon- any of the 
metals except aluminum. 

Composition of Hydrochloric Acid. 

Experiment no. — If the second bottle used in Experiment 94, was 
strong enough to stand the explosion without breaking, open it with 
its mouth under mercury. Notice that no mercury enters the bottle 
and that no gas escapes. Try it with the third bottle used in that 
experiment. Then test the contents of the bottles with moistened 
blue litmus-paper. The reddening of the paper shows that we have 
an acid ; it is HC1. We have shown that the volume of the acid is 
the same as that of the gases that united to form it. How was this 
shown ? 

Experiment 11 1. — Half fill a U- or a V-shaped tube with HC1. 
Through each of two corks pass a wire attached to a strip of plati- 
num. Insert the corks snugly, push the wires down until the plati- 
num strips are nearly immersed in the acid liquid, and connect the 
wires with the poles of a galvanic battery. At the end of four or five 



110 



THE HALOGEN GROUP. 




minutes, remove the cork that carries the negative electrode and 

apply a lighted match. Hy- 
drogen was present, mixed 
with the air that was in that 
arm of the tube at the begin- 
ning of the experiment. Ke- 
move the other cork and 
thrust a bit of moistened 
litin us-paper into that arm of 
the tube. The bleaching of 
the paper and the peculiar 
odor show the presence of 
chlorine. Of course, delivery- 
tubes may be provided for the corks and the gases collected separately. 
See Fig. 5. Exact experiments of this kind are difficult on account 
of the solubility of chlorine in water, but when made they show that 
equal volumes of hydrogen and of chlorine are liberated. 

Experiment 112. — Fill a small graduated tube with pure, dry, hy- 
drochloric acid gas over mercury contained in a proper trough. Into 
the tube thus containing the gas, introduce a piece of potassium 
weighing one or two grams. The metal will take the chlorine from 
the acid to form solid potassium chloride, leaving the hydrogen free. 



Fig. 44. 



K 2 



2HC1 = 2KC1 -f H 2 . 



The volume of the remaining hydrogen ought to be just half the 
volume originally measured by the acid gas. 

Experiment 113. — If a mixture of equal volumes of hydrogen and 
chlorine confined over mercury is exploded in the manner described 
in Experiment 50, and the product of the chemical union is allowed 
to cool to the initial temperature, it will be found that there has been 
no change of the gaseous volume. The litmus test will show that an 
acid has been formed. Other tests would show that none of either 
of the mixed gases has been left free. 

113. Volumetric Composition. — In the preparation of 
hydrochloric acid by the direct union of hydrogen and 
chlorine, one volume of hydrogen combines with one 
volume of chlorine to form two volumes of hydrochloric 



HYDROCHLORIC ACID. Ill 

acid gas. The composition may be graphically repre- 
sented as follows : 



H 

1 


+ 


CI 

35.2 



HC1 



The chemical action effects neither a volumetric nor a 
gravimetric change, but it does effect a thermometric 
change. 

114. Uses. — -Hydrochloric acid is used in the manu- 
facture of chlorine, bleaching-powder, ammonium chloride, 
and many other chlorine compounds. It is of very fre- 
quent use in the chemical laboratory and has become 
almost indispensable in the manufacturing arts. It acts 
directly upon most of the metals, forming metallic chlo- 
rides, e.g., zinc chloride. 

Tests for Hydrochloric Acid. 

Experiment 114. — Dissolve a few crystals of silver nitrate (Ag\N"0 3 ) 
in water. Add a few drops of a solution of sodium chloride (common 
salt, XaCl). A white curdy precipitate of silver chloride (AgCl) is 
formed. 

Experiment 115. — Wash the AgCl obtained in the last experiment 
and try to dissolve it in nitric acid. It is insoluble. 

Experiment 116. —Wash the AgCl of the last experiment and treat 
it with strong ammonia-water* It dissolves. 

115. Tests. — Hydrochloric acid gas may be detected 
by its reddening moistened blue litmus-paper and its form- 
ing dense fumes of ammonium chloride when brought 
into contact with ammonia gas (see Experiment 8). Its 
aqueous solution may be detected by its reddening blue 
litmus-paper and forming, with a solution of silver nitrate, 



112 THE HALOGEN GROUP. 

a white precipitate (AgCl) that is soluble in ammonia- 
water but insoluble in nitric acid. This is a test for all 
chlorides. 

EXERCISES. 

1. When ammonium chloride (sal ammoniac, NH 4 C1) is acted upon 
by sulphuric acid, we have a reaction partly represented as follows: 

2NH 4 C1 + H 2 S0 4 = (NH 4 ) 2 S0 4 + 

See § 141 («)• Complete the equation. 

2. A strip of paper moistened with a certain solution and exposed 
to chlorine turns blue. («) What is the solution? (/>) Explain the 
reaction, (e) What other gas will produce the same change of color? 

3. Define and illustrate valence. 

4. What is a chemical experiment? 

5. Write the chemical formula for the most abundant source of 
chlorine. 

6. How many kinds of atoms are involved in the reaction repre- 
sented in Exercise 1 above? How many atoms are represented in the 
first member of the completed equation? In the second member? 
How many atonrs of each kind are represented in the first member? 
Should the completed equation show the same number of each kind 
in the second member ? 

7. In what way does the presence of moisture aid the. bleaching 
action of chlorine? 

8. What is litmus-paper and what are its laboratory uses? 

9. In what way may hydrochloric acid be prepared from water and 
chlorine? Write the reaction. 

10. Write, in tabular form, the molecular symbols for the oxides, 
the chlorides, the iodides, the nitrates, and the sulphates of the dyad 
metals, Zn, Ca, Mg, Cd, and Hg. 



III. OTHER CHLORINE COMPOUNDS. 

Experiment 117. — Pulverize separate};/ 1 grain of sugar and 1 gram 
of potassium chlorate (KC10„). If they were ground together, there 
would be danger of an explosion. Mix them intimately upon a piece 
of paper and, from a glass rod dipped in sulphuric acid (H 2 S0 4 ), let a 



OTHER CHLORINE COMPOUNDS. 



113 



drop of acid fall upon the mixture. The 
chlorine tetroxide (C1,0 4 ) thus set free causes 
an energetic combustion. 

Experiment 118. — Tn a test-glass, place 1 
gram of potassium chlorate (not pulverized). 
Add a few small pieces of phosphorus and 
nearly fill the glass with water. By means of 
a pipette, bring sulphuric acid into contact 
with the KCIO3. The phosphorus burns under 
water in the C1 2 4 thus set free. 



116. Chlorine Oxides. — Chlorine does not unite directly 

with oxygen, but it may be made to do so by indirect 

means. 

(a) Five oxides of chlorine are theoretically possible, of which 
only three have been isolated. 




(1) Chlorine monoxide (hypochlorous oxide) 

(2) Chlorine trioxide (chlorous oxide) . . 

(3) Chlorine tetroxide (chloryl) 

(4) Chlorine pentoxide (chloric oxide) . . 

(5) Chlorine heptoxide (perchloric oxide) . 



C1,0. 

cuo 3 . 

CL,0 5 . 
CLO r . 



(6) Chlorine monoxide is an explosive, yellow gas, formed by pass- 
ing dry chlorine over mercuric oxide : 

2C1 2 + 2 HgO = Hg 2 OCl 2 + C1 2 0. 

It liquefies at - 20°. 

Chlorine trioxide is a greenish, yellow, unstable gas, prepared by 
the reduction of chloric acid, thus : 

2HC10 3 + X,0 3 = C1 2 3 + 2HX0 3 . 

Chlorine tetroxide is an explosive gas obtained by the action of 

sulphuric acid upon potassium chlorate. It is sometimes called free 

chloryl, the molecule being considered as composed of two compound 

radicals : 

O O 

= Cl = O or (CIO,)', thus : CI - CI or (CIO,) -(CICy). 

1 <f X 

SCHOOL CHEMISTRT — 8 



114 THE HALOGEN GROUP. 

C1 2 5 and Cl 2 O r have not yet been isolated, but their compounds 
are known. 

(c) Note the varying valence of the chlorine in these several oxides, 
and that it is represented by the series of odd numbers, 1, 3, 5, and 7. 

117. Chlorine Acids. — From four of these chlorine 
oxides results a corresponding list of acids and salts. 
The molecular formulas for the acids may be obtained 
from those of the corresponding oxides. 

(«) The addition of H.,0 to the formula of the oxide will give 
double the formula of the acid : 

C1 2 + H 2 = H,C1,0 2 = 2HC10, hypochlorous acid. 
C1 2 3 + H 2 = H,C1 2 4 = 2HC10 2 , chlorous acid. 
C1 2 5 + H 2 = H 2 C1 2 6 = 2HC10 3 , chloric acid. 
C1 2 7 + H 2 = H 2 C1 2 8 = 2HC10 4 , perchloric acid. 

(b) The most important of these acids are HCIO, because of its 
relation to calcium hypochlorite, and HClOo, because of its relation 
to potassium chlorate, two salts of commercial importance. 

Potassium Chlorate. 

Experiment 119. — Repeat Experiment 5. 

Experiment 120. — Repeat Experiment 117. 

Experiment 121. — Repeat Experiment 3. The mixture may be 
placed in a paper or a metal cylinder and the experiment made in 
a dark room with good effect. 

Experiment 122. — Place a pinch of powdered potassium chlorate 
and one of flowers of sulphur in a mortar and rub them together with 
a pestle. A series of explosions will take place. A minute quantity 
of the same mixture may be exploded by a blow of a hammer. 

118. Potassium Chlorate. — Potassium chlorate (chlorate 
of potash, KCIO3) is made by electrolyzing a solution of 



OTHER CHLORINE COMPOUNDS. 115 

potassium chloride. It is largely used in the preparation 
of oxygen, and for other purposes in the laboratory. Ik 
is also used in medicine, in calico printing, and in the 
manufacture of fireworks and friction-matches. It is 
chiefly valuable as an oxidizing agent. 

Aqua Regia. 

Experiment 123. — Put a small piece (4 or 5 sq. cm.) of gold-leaf 
into a test-tube and pour in strong nitric acid until the tube is a 
third full. Put a similar piece of gold-leaf into another test-tube 
and pour in a like quantity of hydrochloric acid. Gently heat the 
contents of each test-tube. If the leaf is gold-leaf, neither liquid will 
dissolve it. Pour the contents of one tube into the other. The gold- 
leaf will quickly dissolve in the mixed acids. 

119. Aqua Regia. — Gold and platinum are insoluble in 
nitric or in hydrochloric acid, but are easily soluble in a 
warm mixture of these acids, especially when heated in the 
mixture. The acids react upon each other, chlorine is set 
free and, in the " nascent " condition, acts upon the metal 
or metallic compound more energetically than it would 
otherwise do. 

(a) The name " aqua regia " (royal water) was given by the old 
alchemists because the mixture was able to dissolve gold, the " king of 
metals." 

(b) The expression " nascent " state or condition is used to describe 
the condition of a chemical agent at the moment it is set free from 
some compound. The most marked effect is greatly increased 
chemical energy. We shall see other cases in illustration as we 
proceed. 

(c) It is probable that "nascent" chlorine is in the atomic condi- 
tion and ordinary chlorine in the molecular condition. They might 
be symbolized as follows : CI and Cl 2 ; or CI - and CI - CI. A certain 
amount of energy is necessary to separate the atoms of a molecule, so 
that molecules act less vigorously than atoms do. 



116 THE HALOGEN GROUP. 

EXERCISES. 

1. What chlorine oxide has trivalent chlorine? 

2. (a) Write the graphic symbol for chloric acid, (b) What is 
the valence of the chlorine? 

3. («) Write the graphic symbol for HC10 4 . (//) What is fch« 
valence of the chlorine? 

4. Read aloud the following equation : KX0 3 + H.,S0 4 = KHS0 4 
+ HXO,,. 

5. («) If 20 liters of hydrogen are exploded with oxygen, how 
many liters of oxygen will be required? (//) How many liters of dry 
steam will be produced ? 

6. (a) If 15 liters of hydrogen are mixed with 10 liters of oxy- 
gen and the mixture is exploded, how many liters of dry steam will be 
produced? (/>) Will any elementary gas remain free? If so, give its 
name and volume. 

7. («) How many grams of hydrogen are there in 3G grams of 
water? (b) How many grams of oxygen? (c) How many liters of 
hydrogen ? (V/) How many liters of oxygen ? 

8. (a) 24 liters of oxygen will yield how many liters of ozone ? 
(b) 30 liters of ozone is equal to how many liters of oxygen? 

9. Why should CI — or II — have greater affinity for another ele- 
ment than CI - CI or H - H ? 

10. (a) How many kinds of atoms are known? (b) How many 
kinds of molecules? 

11. Describe the experiment that may be fairly summarized by the 
equation given in Exercise 4 above. 

12. Nitrohydrochloric acid dissolves platinum. What is the more 
common name for this acid? 

IV. FLUORINE, BROMINE, IODINE, AND MANGANESE. 
Fluorine : symbol, F ; atomic weight, 19; valence, 1. 

120. Source. — Fluorine occurs in nature as a con- 
stituent of fluor-spar (calcium fluoride, CaF 2 ), and of 
cryolite (sodium and aluminum fluorides). It has also 
been found in minute quantities in the teeth, bones, and 
blood of animals. 



FLUORINE, BROMINE, IODINE, AND MANGANESE. 117 

(«) Fluor-spar is ar mineral found somewhat abundantly in nature. 
Cryolite is found in large quantities only in Greenland. 

121. Properties. — Fluorine is a greenish yellow gas, 
and. one of the few elements that form no compound 
with oxygen ; it attacks almost every other known sub- 
stance. Owing to its intense chemical activity, it is 
difficult to prepare. Because of its attraction for almost 
all substances, it can be kept only in vessels made of 
platinum or of a fluoride. It is liberated by electrolyzing 
cold, anhydrous hydrofluoric acid to which some sodium 
fluoride (XaF) has been added. The properties of fluor- 
ine are remarkable. In it boron and quartz crystals 
burn at the ordinary temperature, and organic substances 
are carbonized or inflamed. It unites with various ele- 
ments to form fluorides and decomposes water yielding 
hydrofluoric acid and ozone. Its compounds resemble 
those of chlorine, bromine, and iodine. It liquefies at 
— 187°. As a liquid, at this temperature it loses most of 
its chemical activity, and may be kept in glass or metal 
vessels without change. 

Hydrofluoric Acid. 

Experiment 124. — Rub a heated piece of glass with beeswax or 
paraffin. If the glass is hot enough to melt the wax, it may easily 
have one of its surfaces covered with a thin layer of nearly uniform 
thickness. Let the glass cool. If the coating is not satisfactorily 
uniform, it may be improved with a hot spatula-blade. With any 
pointed instrument, write a name or draw a design, being careful 
that every stroke cuts through to the glass below. In a small tray 
made of lead (platinum is better, but a saucer that you are willing to 
spoil will answer), mix a spoonful of powdered fluor-spar or of cryolite 
with enough sulphuric acid to make a thin paste. Place the prepared 
glass (coated side down) over the tray; heat the tray gently (not 



118 THE HALOGEN GROUP. 

enough to melt the wax) and set it aside in a warm place for a day. 
Do not inhale the acid fames. Clean the glass by scraping it and rub- 
bing with turpentine if you used beeswax, or with hot water if you 
used paraffin. The name or design will be seen etched upon the 
glass. 

Experiment 125. — Upon a pane of glass that will fit the window of 
your chemical laboratory, or the glass front of one of your laboratory 
cases, etch the proper designation of the class, the date, and the 
autographs of the individual members of the class. The "class 
artist " may add an appropriate border and emblematic designs. 

122. Hydrofluoric Acid. — This acid (HF) is distin- 
guished from all other substances by its power of cor- 
roding glass. It corresponds closely to the other haloid 
acids (i.e., HC1, HBr, and HI), but it is more energetic 
than any of them. It is readily prepared, as above, by 
distilling some fluoride with sulphuric acid, e.g., 

CaF 2 + H,S0 4 = CaS0 4 -f 2HF. 

(a) The reaction is closely analogous to that for the distillation of 
NaCl with H,S0 4 (§110, a). The solution of HF is also used for 
etching glass. The dry acid does not act on glass, but the slightest 
trace of water renders it capable of doing so. Its aqueous solution 
is an article of commerce. 

Bromine: symbol, Br ; density at 0°, 3.188 ; atomic weight, 80 ; 
valence, 1, 5, 7. 

123. Source. — Bromine does not occur free in nature, 
but is found combined with metals, especially as magne- 
sium bromide, in sea-water and in the water of certain 
salt- wells and springs. 

(a) Much of the bromine made in the United States comes from 
the salt-wells of Ohio, West Virginia, and Michigan. The bittern 
that remains after the crystallization of the sodium chloride contains 
magnesium bromide in such quantities that bromine is profitably 



FLUORINE, BROMINE, IODINE, AND MANGANESE. 119 

extracted from it. The bittern is treated with sulphuric acid and 
potassium chlorate or manganese dioxide in stone retorts and heated 
with steam, when the free bromine distils into a cold receiver. 

MgBr 2 + MnO a + 2H 2 S0 4 = MnS0 4 + MgS0 4 + Br + 2H 2 0. 

The name bromine is derived from the Greek bromos, meaning a 
stench. 

Properties of Bromine. 

Experiment 126. — Into a flask of two or three liters capacity, put a 
few drops of bromine, and cover the flask loosely. In a few minutes 
the jar will be filled with the heavy red vapor of bromine. 

Experiment 127. — Into the jar of vaporized bromine, introduce a 
strip of moistened litmus- or turmeric-paper. It will be bleached. 

Experiment 128. — Add a few more drops of bromine, and after it 
has vaporized, introduce a thin slice of dry phosphorus. It will ignite. 

Experiment i2g. — Into a tall jar filled with bromine vapor, let fall 
a few freshly prepared filings of metallic antimony. The result is 
much like that of Experiment 90. 

124. Properties, etc. — Bromine is a dark red liquid of 
disagreeable odor, very volatile at ordinary temperatures, 
and extremely corrosive. It is sparingly soluble in water 
and easily soluble in ether, carbon clisulphide, or chloro- 
form. Its vapor has a density of 80, being more than 
five times as heavy as air. Its chemical properties closely 
resemble those of chlorine, but it is less active. Its attrac- 
tion for hydrogen fits it for bleaching and disinfecting 
uses. Some of the bromides are' used in medicine and 
photography. 

(a) Bromine forms acids as follows: hydrobromic, HBr; hypo- 
bromous, HBrO ; bromic, HBr0 3 ; perbromic, HBr0 4 . They closely 
resemble the corresponding chlorine compounds. 

(b) Bromine, when swallowed, acts as an irritant poison; when 
dropped upon the skin it produces a sore that is very difficult to heal. 
The best antidote for its corrosive action is some substance that takes 
up oxygen readily, as sulphurous oxide (S0 2 ), or a sulphite. 



120 THE HALOGEN GROUP. 

Iodine : symbol, I ; density, 4.95 ; atomic weight, 126 ; valence, 1, 3, 5, 7. 

125. Source. — Iodine compounds exist in vejy minute 
quantities in the water of the sea and of some saline 
springs. From sea-water, the iodide is absorbed by cer- 
tain marine plants. The ashes (kelp) of these seaweeds 
contain sodium and magnesium iodides. Iodine is ob- 
tained by heating the kelp with water, concentrating this 
solution until most of the less soluble salts are removed, 
and treating the resulting liquid with sulphuric acid and 
manganese dioxide. Iodine is set free in the form of a 
beautiful violet-colored vapor that soon condenses to a 
solid. At present, the principal source of iodine is the 
niter beds of Chile and Peru, where it occurs as sodium 
iodate (NaI0 3 ). After separating the iodate from the 
nitrate, the iodine is set free by sulphurous acid. 

Properties of Iodine. 

Experiment 130. — Put about 0.1 of a gram of iodine 1 into a dry 
test-tube. Heat the test-tube in a flame and notice that the crystals 
vaporize without visible liquefaction. Notice that the vapor is very 
heavy as well as very beautiful. If the upper part of the tube is cold, 
minute iodine crystals will coudense there. 

Experiment 131. — Prepare some starch paste, as in Experiment 102, 
and dilute 5 or 6 drops of it with 10 cu. cm. of water. Dissolve a very 
small piece of iodine in alcohol and add a drop of the alcoholic solution 
(tincture) .to the dilute starch. The starch will be colored blue even 
when the tincture is very dilute. The blue color will disappear upon 
heating the solution and reappear upon cooling it. 

Experiment 132. — Drop a few crystals of iodine into a large bottle. 
Dip a strip of white paper into the colorless starch paste and suspend 

1 In weighing iodine, place it on a small piece of thin paper or glass. 
Do not let it come into contact with a metal scale-pan. 



FLUORINE, BROMINE, IODINE, AND MANGANESE. 121 

it in the bottle. The paper maybe held in place by the stopper of the 
bottle. As the iodine sublimes and diffuses through the bottle, it 
soon comes into contact with the starch and colors the paper blue. 
Starch will detect the presence of one part of iodine in 300,000 parts 
of water. 

Experiment 133. — Add a few drops of the alcoholic solution pre- 
pared in Experiment 131 to 10 cu. cm. of water in a test-tnbe. Owing 
to the sparing solubility of iodine in water, most of the iodine will be 
precipitated. Pour 5 cu. cm. of this aqueous solution into a test-tube, 
add 8 or 10 drops of carbon disulphide (CS 2 ), and shake the contents 
of the tube. On standing for a few moments, the disulphide will set- 
tle to the bottom, when it will be seen to be colored purple-red ; its color 
is due to the iodine dissolved in it. Carbon disulphide will detect the 
presence of one part of iodine in 1,000,000 parts of water. 

Experiment 134. — Pour 10 cu. cm. of water into each of three tall 
test-glasses. Add a few drops of a solution of potassium iodide to 
each. To the first, add a few drops of a solution of lead acetate 
(sugar of lead) . Brilliant yellow lead iodide is formed. To the second, 
add a few drops of a solution of mercurous nitrate. Yellowish green 
mercurous iodide is formed. To the third, add a few drops of a solu- 
tion of mercuric chloride (corrosive sublimate). Scarlet mercuric 
iodide is formed. 

126. Properties, etc. — Iodine is a blue-black, crystalline 
solid having a metallic luster. Its vapor is very heavy, 
having a density of about 126. Iodine is very sparingly 
soluble in water but readily dissolves in alcohol, ether, 
chloroform, carbon disulphide, or aqueous solutions of the 
metallic iodides. The chemical activity of this element is 
less than that of bromine. Iodine is used in medicine, 
photography, and the manufacture of aniline-green. The 
blue color it forms with starch, its beautifully colored 
vapor, and the purple-red color it forms with carbon disul- 
phide form delicate tests for free iodine. 

(a) Iodine forms acids as follows: hydriodic, HI; iodic acid, 
H10 3 ; periodic acid, H 3 TO fi . They closely resemble the corresponding 
chlorine and bromine compounds. 



122 



THE HALOGEN GROUP. 



127. The Halogen Group. — Fluorine, chlorine, bromine, 
and iodine constitute a remarkable natural group. They 
exhibit a marked gradation in properties and close analo- 
gies in their elementary condition and in their correspond- 
ing compounds (see § 148). 

(a) Concerning their gradation of properties : 

1. At the ordinary temperature, fluorine is a gas; chlorine is a 
gas; bromine is a liquid, and iodine is a solid. 

2. Liquid chlorine is transparent ; bromine is but slightly so ; 
iodine is opaque. 

3. Chlorine has a density of 35.2 ; bromine vapor, 80 ; iodine vapor, 
126. 

4. Fluorine has an atomic weight of 19 ; chlorine, 35.2 ; bromine, 
80; iodine, 126. 

5. Generally speaking, their chemical activities are graded in the 
inverse order, being greatest in the case of fluorine, less in chlorine'; 
still less in bromine, and least in iodine. (In the case of such natural 
groups the chemical activities frequently vary inversely as the atomic 
weights.) The atomic weight of bromine is nearly the arithmetical 
mean of those of chlorine and iodine ; in general chemical deportment, 
bromine stands midway between the other two elements. 

(6) Concerning their analogies : 

1. Their binary compounds with potassium and sodium resemble 
common salt. Hence, these compounds are called haloid salts and 
these elements, halogens (Greek, halos, salt and gennao, I produce). 

2. Each of them combines with hydrogen, volume to volume and 
without condensation, to form the haloid acids. 

3. These acids have a great attraction for water. Their aqueous 
solutions have the same chemical properties as the acids. 

(c) Recapitulation : 





Fl 


CI 


Br 


I 


Atomic weight . 


19 


35.2 


79.96 


126.85 


Fusing-point . . 




-102° 


- 72° 


+ 114° 


Boiling-point . . 


-187° 


- 33° 


+ 60° 


+ 184° 


Densitv .... 


1.14 


1.47 


3.18 


4.96 


Color .... 


greenish 
yellow 


yellowish 
green 


brown 


black 



FLUORINE, BROMINE, IODINE, AND MANGANESE. 123 

Manganese : symbol, Mn ; density, ,7.2 ; atomic weight, 55 ; valence, 2, 
3, 4, 6, 7. 

128. Manganese. — The principal source of manganese 
is the dioxide (Mn0 2 ) which is found in nature as the 
mineral pyrolusite. Among the other manganese ores are 
braunite (Mn 2 3 ) and hausmanite (Mn 3 4 ). The metal 
is seldom prepared, but may be obtained by heating one of 
the oxides with carbon at an intense white heat for several 
hours, and in other ways. It is very hard and brittle, 
easily soluble in dilute acids, and decomposes warm water 
with the evolution of hydrogen. When pure, it is almost 
as infusible as platinum and oxidizes easily in the air. 
It is best kept in petroleum. It is feebly magnetic and 
forms a beautiful alloy with copper. The metal is used 
as an alloy of iron in the manufacture of steel. 

Note. — Manganese has certain properties that ally it to chromium, 
iron, nickel, cobalt, and copper, so that these six metals are sometimes 
grouped as a family. Their atomic weights lie nearly together, and 
they all belong to the fourth series in the periodic system (§ 148, b). 
Because of other characteristics, manganese is here grouped with the 
halogens. 

Manganese Oxide. 

Experiment 135. — Put a small quantity of manganese dioxide into 
an ignition-tube and add enough sulphuric acid to wet it thoroughly. 
Support the tube in a slanting position and heat it gently. Collect 
the gas, and find out what it is. 

129. Oxides. — At least five distinct manganese oxides 
are known : 

(a) Manganese monoxide (manganous oxide, MnO) is powerfully 
basic. 

(b) Red oxide of manganese (mangano-manganic oxide, Mn 3 4 ) 
may be considered a compound of MnO and Mn 2 3 . It is analogous 
to magnetic iron ore. 



124 THE HALOGEN GROUP. 

(c) Manganese sesquioxide (manganic oxide, Mn 2 G ? ) is the mineral 
braunite. It is isomorphous with A1 2 3 and Fe 2 O g . The correspond- 
ing hydroxide [Mn 2 2 (OH) 2 ] is found in nature as manganite, or gray 
manganese ore. 

(d) Manganese dioxide (manganese peroxide, black oxide of man- 
ganese, Mn0 2 ) is the most important manganese ore. It is used in 
preparing oxygen and chlorine, and in coloring and decolorizing glass. 
At a bright red heat, it gives up oxygen and is reduced to Mn 3 () 4 . In 
the preparation of chlorine from hydrochloric acid and manganese 
dioxide (see Experiment 86), large quantities of the practically worth- 
less manganous chloride are produced. The Weldon process for the 
utilization of this product is, in effect, a regeneration of the Mn0 2 . 
When a solution of the manganous chloride is treated with lime, the 
following reaction takes place: 

MnCl 2 + Ca(OH) 2 = Mn(OH) 2 + CaCl 2 . 

When this manganous hydroxide is mixed with lime, and treated 
with steam and air, one of the following reactions takes place : 

Mn(OH) 2 + Ca(OII) 2 + O = CaMn0 3 + 2H 2 G; or 
2Mn(OH) 2 + Ca(OH), + 2 = CaMn 2 5 + 3II 2 0. 

These calcium compounds may be regarded as mixtures of lime and 

manganese dioxide. 

CaMn0 3 = CaO, Mn0 2 . 

CaMn 2 0, = CaO, 2Mn0 2 . 

The treatment of either of them with hydrochloric acid yields chlorine. 

(e) Manganic anhydride (MnO s ) and manganic acid (H s Mn0 4 ) 
have not yet been isolated, but several manganates (e.g., K 2 Mn0 4 ) are 
well known. 

(/) Manganese heptoxide (Mn.,() 7 ) is an anhydride, yielding per- 
manganic acid (HMn0 4 ) when brought into contact with water. 

Manganese Salts. 

Experiment 136. — Dissolve 0.5 of a gram of oxalic acid (C 2 II 2 4 ) 
crystals in 50 cu. cm. of water ; add 5 cu. cm. of sulphuric acid ; warm 
to about 60°. To this colorless solution, add, drop by drop, a solution 
of potassium permanganate (KMn0 4 ). The KMnG 4 gives up oxygen 
and converts the C 2 II 2 4 to H 2 and C0 2 , and is reduced to MnS0 4 
and K 2 S0 4 , in which process, its rich color is destroyed. If an excess 
of the potassium permanganate is added, it will not be decolorized. 



FLUORINE, BROMINE, IODINE, AND MANGANESE. 125 

Experiment 137. — Repeat the last experiment, using ferrous sul- 
phate (FeS0 4 ) instead of C 2 H 2 4 . The KMu0 4 oxidizes the ferrous 
to ferric sulphate. 

Note. — Knowing the reactions for these experiments and the 
quantity of KMn0 4 used before the decoloration ceases, the quantity 
of oxidizable matter (C 2 H 2 () 4 or FeS0 4 ) present is easily calculated 
(quantitative analysis) . 

Experiment 138. — Mix some KMn0 4 and barium dioxide (Ba0 2 ) 
in a mortar. Transfer the mixture to a flask and moisten it with 
sulphuric acid. A starch and potassium iodide test-paper held at the 
mouth of the flask will be colored blue. Explain the discoloration. 

130. Manganese Salts. — A few years ago, the man- 
ganates and permanganates were found only in the 
laboratory where they were used as oxidizing agents. 
They are now manufactured on the large scale for use 
as disinfectants. 

EXERCISES. 

1. Give two of the most marked physical properties of hydrogen, 
and two of its distinctive chemical properties. 

2. What is a triad ? A pentad ? A quadrivalent atom ? A biva- 
lent compound radical ? Illustrate each. 

3. By passing the vapor of iodine with hydrogen over platinum 
sponge heated to redness, a strongly acid gas is synthetically formed. 
What is its name, its molecular weight, and its density ? 

4. A large jar, about a quarter full of ble aching-powder had been 
standing for some time until the upper part contained a gas given 
off by the chloride. Into this gas, a moistened slip of paper was 
thrust. The paper was instantly colored deep blue. What was the 
gas and with what was the test-paper moistened? Explain the 
phenomenon. 

5. What analogies exist between members of the halogen group ? 

6. Symbolize the chlorides, bromides, iodides, chlorates, bromates, 
and iodates of the following : K', Na', Ag', Cu", Zn", An'", Pt iv . 

7. How is tincture of iodine prepared ? 

8. How many products of the combustion of hydrogen in air can 
you name ? 



126 THE HALOGEN GROUP. 

9. Name and symbolize a gaseous compound that is most con- 
veniently prepared by the action of strong sulphuric acid upon 
common salt. 

10. Describe in two words a chemical reaction that results only in 
the synthesis of water. 

11. You have had an experiment involving the process of sub- 
limation. Describe the experiment. 

12. Pyrolusite may be reduced to Mn 3 4 by intense heat. Write 
the reaction. 

13. Write a graphic formula for K 3 Mn0 4 . 

14. Write two graphic formulas for KMn0 4 . 

15. Write a graphic formula for manganese sesquioxide, repre- 
senting the metal as a dyad. 

16. Write a graphic formula for Mn"0 3 . 






CHAPTER VIII. 

ATOMIC AND MOLECULAR WEIGHTS, ETC. 

131. Combining Weights of Elements. — A study of the 
figures that represent the quantitative composition of 
chemical compounds shows that there exists between them 
such a relation that if a fixed quantity of one of the con- 
stituent elements is taken, and the quantities of the ele- 
ments that combine therewith are noted, there will be a 
remarkable repetition of the same figures (or of simple 
multiples thereof) for each of the elements examined. 

(a) For instance, if we weigh the component parts of certain com- 
pounds, we find that : 

1 part of hydrogen combines with 19 parts of fluorine. 

1 part of hydrogen combines with 35.2 parts of chlorine. 

1 part of hydrogen combines with 80 parts of bromine. 

1 part of hydrogen combines with 126 parts of iodine. 

23 parts of sodium combine with 19 parts of fluorine. 

23 parts of sodium combine with 35.2 parts of chlorine. 

23 parts of sodium combine with 80 parts of bromine. ' 

23 parts of sodium combine with 126 parts of iodine. 

7 parts of lithium combine with 19 parts of fluorine. 

7 parts of lithium combine with 35.2 parts of chlorine. 

7 parts of lithium combine with 80 parts of bromine. 

7 parts of lithium combine with 126 parts of iodine. 

39 parts of potassium combine with 19 parts of fluorine. 
39 parts of potassium combine with 35.2 parts of chlorine. 
39 parts of potassium combine with 80 parts of bromine. 
39 parts of potassium combine with 126 parts of iodine. 
127 



128 ATOMIC AND MOLECULAR WEIGHTS, ETC. 

16 parts of oxygen combine with 56 parts of iron. 

16 parts of oxygen combine with 206 parts of lead. 

16 parts of oxygen combine with 112 parts of cadmium. 

16 parts of oxygen combine with 65 parts of zinc. 

16 parts of oxygen combine with 24 parts of magnesium. 

32 parts of sulphur combine with 56 parts of iron. 

32 parts of sulphur combine with 206 parts of lead. 

32 parts of sulphur combine with 112 parts of cadmium. 

32 parts of sulphur combine with 65 parts of zinc. 

32 parts of sulphur combine with 24 parts of magnesium. 

(b) Careful study of the above table shows that the figures that 
represent the relative weights of the elements that combine with one 
part of hydrogen also represent the weights of the same elements that 
combine with 23 parts of sodium, 7 parts of lithium, and 39 parts of 
potassium; and that 16 parts of oxygen combine with the same rela- 
tive weights of the five given elements as do 32 parts of sulphur. 
The list might be extended so as to include all the elements. As 
hydrogen enters into combination in the smallest proportion of any, 
its combining weight is taken as unity; the weight of the quantity 
of any other substance that unites with one weight of hydrogen is 
called the combining weight or the equivalent w T eight of that 
element. 

(c) Some elements do not combine with hydrogen. The combin- 
ing weight of each of these elements is ascertained by determining 
the weight of the quantity of that element that unites with the 
known combining weight of some other element. In the examples 
above given it is seen, by direct comparison with hydrogen, that the 
combining weight of fluorine is 19; of chlorine, 35.2; of bromine, 80; 
and of iodine, 126. Sodium, lithium, and potassium do not unite 
readily with hydrogen and so their combining weights are determined 
by indirect comparison with hydrogen. The combining weights of 
each of the four elements just mentioned unite with a uniform quan- 
tity of each of these three elements. Thus we learn that the com- 
bining weight of sodium is 23; of lithium, 7; and of potassium. 39. 
All elements unite with other elements in proportion to their com- 
bining weights or to some simple multiple thereof. 



ATOMIC AND MOLECULAR WEIGHTS, ETC. 129 

132. The Atomic Theory. — Up to the beginning of the 
nineteenth century, there were two guesses as to the ulti- 
mate constitution of matter. One of these assumed that 
there was no limit to the divisibility of matter. But the 
Greek philosophers thought that there was a limit beyond 
which a substance could not be divided. The ultimate 
particles thus assumed to exist were named atoms, a word 
signifying indivisible. When John Dalton discovered the 
law of definite proportions (§ 77), it occurred to him that 
if this hypothesis of the Greek philosophers was true, it 
would explain both the law of definite proportions and 
that of multiple proportions (§ 78). The atomic theory, 
as now understood, may be stated thus : 

All substances are composed of minute, ultimate particles 
that can not be divided without destroying the identity of 
the substance. For any given substance, these particles 
are alike in size, shape, and weight. The relative iveights 
of these ultimate particles may be ascertained from the 
relative weights in which the substances combine with one 
another. All the known facts of chemistry agree with this 
theory. 

(a) If the atoms of any element are exactly alike, and differ in 
weight from the atoms of other elements, and if the differing atoms 
of a compound always unite in the same ratio to form that compound, 
these facts explain the law of definite proportions. Thus, if sodium 
and chlorine unite, one atom of the former with one atom of the 
latter, to form sodium chloride, and if all the sodium atoms have 
the same weight, and all the chlorine atoms have the same weight, 
then sodium chloride, wherever found, will always have exactly the 
same composition by weight, complying thus with the law of definite 
proportions. In other words, if matter consists of atoms having 
definite weights, and if chemical reactions always take place between 
definite numbers of these atoms, then chemical action always takes 

SCHOOL CHEMISTRY — 9 



130 ATOMIC AND MOLECULAR WEIGHTS, ETC. 

place between definite weights of substances. That substances do 
thus unite is one of the fundamental principles of chemistry. 

(&) If two elements unite in more than one proportion, and one 
atom to one atom, or by one atom to two atoms, or by two atoms to 
three atoms, etc., that is, some simple number of atoms uniting with 
some simple number of other atoms, then the law of multiple pro- 
portions is thereby explained. Assuming that the weight of a nitrogen 
atom is 14, and that the weight of an oxygen atom is 16, and that two 
atoms of nitrogen unite with one atom of oxygen (X 2 0), then the 
weights of the two elements in the nitrogen monoxide are as 28 to 16. 
If one atom of nitrogen unites with one atom of oxygen (XO), then 
the weights of the elements in the nitric oxide are as (14 to 16 or 
as) 28 to 32. Similarly, it is evident that on like suppositions, the 
gravimetric relations of the two elements in the five oxides of nitro- 
gen are 28 parts of nitrogen to 16, 32, 48, 64, and 80 parts of oxygen. 
The weight of the nitrogen being constant, the weights of the oxygen 
in the successive oxides are represented by the ratio numbers, 1, 2, 
3, 4, and 5, as shown by the table in § 78. 

133. Avogadro's Law. — The corner-stone of modern 
chemistry, as distinguished from the chemistry that pre- 
ceded it, is a proposition known as Avogadro's law, the 
evidence in support of which can not be satisfactorily 
presented in this place. It may be stated as follows : 
Equal volumes of all substances in the gaseous condition, the 
temperature and pressure being the same, contain the same 
number of molecules. 

134. Molecular Weights. — The weights of equal volumes 
of different gases may be readily ascertained experimen- 
tally. According to the law of Avogadro, such equal 
volumes contain the same number of molecules. Conse- 
quently, the ratio between the weights of the molecules 
of different gases is the same as the ratio between the 
weights of equal volumes thereof. If, under the same con- 



ATOMIC AND MOLECULAR WEIGHTS, ETC. 131 

ditions of temperature and pressure, a liter of one gas 
weighs eighty times as much as a liter of another gas, 
then the molecule of the first gas must be eighty times as 
heavy as the molecule of the second gas. Hydrogen, the 
lightest known gas, is taken as the standard. Its mole- 
cule consists of two atoms, the weight of each of which 
we take as unity. Accordingly, the molecular weight of 
hydrogen is taken as two, a convention that enables us to 
express molecular and atomic Aveights in the same terms. 
The density of any substance in the gaseous state indi- 
cates the weight of a molecule of that substance with 
respect to the weight of a molecule of hydrogen. But 
as the unit adopted is the weight of the hydrogen atom 
rather than the weight of the hydrogen molecule, it fol- 
lows that the density of a gas must be multiplied by two 
in order to get the molecular weight of that gas. That is 
to say, the molecular weight of any substance is twice its 
vapor-density expressed in terms of the hydrogen standard 
for density. 

(a) Formerly this was the only method known for the determina- 
tion of molecular weights. Hence, the molecular weights of substances 
that could not be volatilized could not be determined directly. Cer- 
tain properties of solutions have now been shown to have relations to 
the molecular weights of the dissolved substances analogous to those 
involved in Avogadro's law, and these relations may be used to deter- 
mine the molecular weights of almost all substances. 

135. Atomic Weights. — Since the weight of the molecule 
equals the sum of the weights of the atoms in the molecule, 
the same unit being used in both cases, it follows that if 
the number of atoms in a molecule is known, the weights 
of the component atoms may be easily ascertained. The 



132 



ATOMIC AND MOLECULAR WEIGHTS, ETC. 



simplest case is that of the molecule of an element. For 
example, the molecular weight of nitrogen is twenty-eight ; 
of oxygen, thirty-two ; of chlorine, seventy and four-tenths ; 
of bromine, 160 ; and of sulphur, sixty -four. Since there 
is good reason for supposing that each of these molecules 
consists of two atoms, the atomic weight is supposed to 
be half of the molecular weight determined as already 
explained. A more general method is to combine the 
analysis of the compounds of an element with the deter- 
mination of the molecular weights of the same compounds. 
This method will be best understood from an example : 

(a) Suppose the chemist wishes to determine the atomic weight of 
oxygen. He begins with steam and finds, from its density, that its 
molecular weight is 18, and, by analysis, that § of this is oxygen. He 
proceeds in this way with all the gaseous or volatile compounds of 
oxygen, and tabulates some of the results, as follows : 





Wkigiit 

OF 


Wkigiit ok Oxygkn in 




MoLKClLE. 


Molecule; 


Water 


H 0" 


18 


16 


16 x 1 


Carbon monoxide 






CO 


28 


16 


16 x 1 


Nitric oxide . . 






NO 


30 


16 


16 x 1 


Alcohol . . . 






C 9 H c O 


46 


16 


16 x 1 


Ether .... 






(C 2 H 5 ) 2 


74 


16 


16 x 1 


Carbon dioxide . 






C0 2 


44 


32 


16 x 2 


Nitrogen peroxide 






N0 2 


46 


32 


16 x 2 


Sulphur dioxide 






S0 2 


64 


32 


16 x 2 


Acetic acid . . 






C 2 H 4 2 


60 


32 


16 x 2 


Sulphur trioxide 






so 3 


80 


48 


16 x 3 


Methyl borate . 






(CII,). 3 B() 3 


104 


48 


16 x 3 


Ethyl borate . . 






(C 2 H,)„B0 3 


146 


48 


16 x 3 


Ethyl silicate . 






CC 2 H.) 4 Si0 4 


208 


64 


16 x 4 


Osmium oxide . 






Os() 4 


254 


64 


16 x 4 


Oxygen 


2 


32 


32 


16 x 2 



ATOMIC AND MOLECULAR WEIGHTS, ETC. 133 

He notices that the smallest weight of oxygen in any of these com- 
pounds is 16, and that all the others are simple multiples of this. He 
can not believe that this is mere chance, especially as he finds similar 
results in determining other atomic weights. The only explanation 
possible is that this 16 is the weight of a definite quantity of oxygen, 
and that it represents the least quantity of oxygen that can enter into 
combination (§ 4). Hence, he concludes that 16 is the atomic weight 
of oxygen, and that the substances analyzed contain respectively one, 
two, three, and four atoms of oxygen to the molecule. Of course, the 
symbols in the second column of the table above can not be determined 
until after the determination of the atomic weights of the elements 
involved. The table also shows that the oxygen molecule consists of 
two atoms. The combining weight of an element is its atomic weight. 



136. Elemental Molecules. — Let us imagine a volume 
of hydrogen that contains 1000 hydrogen molecules. By 
Avogadro's law, the same volume of chlorine contains 
1000 chlorine molecules. By the direct union of these, 
we form two such volumes of hydrochloric acid gas, which, 
according to Avogadro's law, must contain 2000 mole- 
cules. 

1000 H 2 + 1000 Cl 3 = 2000 HC1. 

But each molecule of hydrochloric acid (HC1) contains 
one hydrogen atom and one chlorine atom. Consequently, 
the 2000 acid molecules contain at least 2000 hydrogen 
atoms and 2000 chlorine atoms. Since these 2000 hydro- 
gen atoms of the product are identical with the 1000 
hydrogen molecules of the factor (see § 140), it follows 
that each hydrogen molecule contains at least two atoms, 
or that the hydrogen molecule is diatomic. In the same 
way we see that the chlorine molecule is diatomic. The 
number of atoms in a molecule of most of the elements 
have been determined by this and other methods. 



134 ATOMIC AND MOLECULAR WEIGHTS, ETC. 

(a) The vapor-density and the atomic weight being known, the 
number of atoms in the molecule is easily determined. As the vapor 
of mercury is 100 times as heavy as hydrogen, the mercury molecule 
must, by Avogadro's law, weigh 100 times as much as the hydrogen 
molecule ; i.e., the molecular weight of mercury is 200. As this is the 
same as the atomic weight of this element, we conclude that the mer- 
cury molecule contains only one atom. Similar considerations indicate 
that cadmium also is monatomic. On the other hand, the vapor-den- 
sity of arsenic is 150; its molecular weight' is therefore 300. As the 
atomic weight of arsenic is only 75, we conclude that an arsenic mole- 
cule contains four atoms. Similar considerations lead to the conclusion 
that phosphorus also is tetratomic. 

137. Law of Gay-Lussac. — The ratio in which gases 
combine by volume is always a simple one; the volume of 
the resulting gaseous product bears a simple ratio to the 
volumes of its constituents (see § 78). 

(a) The following modes of volumetric combination illustrate the 
truth and meaning of the law : 

(1) 1 unit volume + 1 unit volume = 2 unit volumes. 
Examples: HC1; HBr; HI; NO. 

Condensation == 0. 

(2) 2 unit volumes -f 1 unit volume = 2 unit volumes. 
Examples: H 2 0; H,S; N 2 ; N0 2 . 

Condensation = \. 

(3) 3 unit volumes -I- 1 unit volume = 2 unit volumes. 
Examples: H 3 N; SO r 

Condensation = £• 
In general, the gaseous product occupies 2 unit volumes. 

EXERCISES. 

1. Show that a molecule of bromine contains two atoms. 

2. Define atom and atomic weight. 

3. What is the difference between the combining weight and the 
atomic weight of an element ? 



ATOMIC AND MOLECULAR WEIGHTS, ETC. 135 

4. What is the standard of atomic weight ? What do we mean 
when we say that the atomic weight of oxygen is 16 ? 

5. If the atomic weight of hydrogen is called five, what should 
we call the atomic weight of nitrogen? 

6. Why can we not weigh different atoms, and thus directly 
determine atomic weights? 

7. State the modern atomic theory. 

8. State the law on which is based the argument that shows that 
chlorine is diatomic. 

9. Under similar conditions, which will occupy the greater space, 
100 molecules of hydrogen or 100 molecules of nitrogen ? 

10. What is the molecular weight of a vapor that is 23 times as 
heavy as hydrogen ? 

11. What is the molecular weight of N 2 0? What is its density? 

12. Define allotropism. Give an illustration of your definition. 

13. How is oxygen prepared on the large scale ? How may it be 
prepared without heat ? 



CHAPTER IX. 
STOICHIOMETRY, ETC. 

138. Reactions and Reagents. — Any change in the com- 
position of a molecule is called a chemical reaction. Sub- 
stances acting in such a chemical change are called reagents. 

(a) Changes in molecular composition are of three kinds : 

(1) Changes in the kind of the constituent atoms. 

(2) Changes in the number of the constituent atoms. 

(3) Changes in the relative positions of the constituent atoms. 

(h) When hydrogen burns in air, the hydrogen and the oxygen 
react upon each other; they are the reagents used to produce a 
molecular change. 

139. Expression of Reactions. — In any given substance 
of homogeneous composition, all the molecules are alike. 
The nature of the mass depends upon the nature of the 
molecule. The mass may be fittingly represented by 
the molecule. Any chemical change in the mass may 
be represented by a corresponding change in the mole- 
cule. Hence, chemical reactions are generally expressed in 
molecular symbols. 

140. Factors and Products. — The molecules that go into 
a reaction are called factors; the molecules that come from 
it are called products. 

(«) In the preparation of hydrogen, the factors were Zn and 
2HC1; the products were ZnCl 2 and H 2 . The total mass of the 
factors is always equal to the total mass of the products. 
136 



STOIC HIOMETRY, ETC. 137 

141. Chemical Equations. — Chemical reactions are com- 
monly and conveniently represented by equations, placing 
the sum of the factors equal to the sum of the products. 

(a) The equality results from the indestructibility of matter. The 
individual atoms of the factors reappear in the products ; they are 
differently arranged, but not one is gained or lost. From this it- 
follows that the equation also shows an equality between the total 
weights of the factors and of the products. 

(b) The equation also represents the relative weights of the several 
substances engaged in the reaction. The equation, H 2 4- O = H 2 0, 
means, literally, that 2 atomic weights of hydrogen united with 16 
atomic weights of oxygen yield 18 such weights of water, but the 
relation is equally true for larger quantities of matter. Thus, we 
learn from it that 2 grams of hydrogen unite with 16 grams of 
oxygen to form 18 grams of water, or that 12 kilograms of hy- 
drogen unite with 96 kilograms of oxygen to form 10S kilograms 
of water. 

(c) Strictly speaking, it is not proper to represent a fractional 
part of a molecule as entering into or resulting from a chemical 
reaction, as we do when w 7 e write H 2 + O = H 2 0. To obviate the 
error of representing an atom of free oxygen, we should indicate 
twice the quantity of each substance, as follows: 2H 2 + 2 = 2H 2 0. 
But, for the sake of convenience, chemists generally write the equa- 
tions in the simpler form, as the gravimetric relations expressed are 
the same. 

(d) When the reacting bodies are gaseous, the equation, written 
in complete molecules, also represents volumetric relations. Remem- 
bering Avogadro's law (§ 133), we easily see that 2H 2 + 2 = 2H 2 
indicates that two (molecular or other) volumes of hydrogen unite 
with one of oxygen to yield two volumes of dry steam ; e.g., two liters 
of hydrogen and one liter of oxygen unite to form two liters of dry 
steam. 

142. Gravimetric Computations. — Knowing the equation 
for any given reaction and the atomic weights of the sev- 
eral elements involved, we are able to solve all problems 
concerning the weight of substances appearing as factors 



138 STOICHIOMETRY, ETC. 

or products. From the data now known and those given 
in the problem, make the following proportion : 

As the number representing the total combining weights of 

the given substance is to the number representing the total 

combining weights of the required substance, so is the actual 

weight of the given substance to the actual weight of the 

required substance. 

(a) These numbers representing combining weights are to be 
derived, of course, from the equation. A few examples are given. 
When a close approximation to exact atomic weights (see Appen- 
dix, § 1) will simplify the computation, such an approximation may 
be permitted in school work. 

(1) How much hydrogen can be obtained from hydrochloric acid 
by using 20 grams of zinc ? 

Solution. — Write the reaction with the combining weights of the 
several reagents. 2(1 + 352) m+fU 

Zn + 2HC1 = ZnCl 2 + H 2 

65 72.4 135.4 2 

Form the proportion according to the above rule : 
65 : 2 : : 20 grams : x grams. 
.-. x — 0.61538 grams, or 615.38 milligrams of H. — Ans. 

(2) How much HC1 will be required? 

65 : 72.4 : : 20 : : x. 

.-. x = 22.27 -|- grams of dry HCL — Ans. 

(3) How much ZnCl 2 will be produced? 

65 : 135.4 : : 20 : x. 

.-. x = 41.66 + grams of ZnCl 2 . — A ns. 

(4) How much ziuc is necessary to prepare 1 Kl. of hydrogen? As 
1 liter of hydrogen weighs 0.09 of a gram, 1000 liters (1 Kl.) of 
hydrogen weigh 90 grams. 

65 : 2 : : x : 90. 

.-. x = 2925 grams or 2.925 Kg. of Zn. — Ans. 



STOICHIOMETRY, ETC. 139 

143. Gas-volumetric Computations. — It follows from 
the law of Avogadro that, in equations where whole 
molecules of gaseous substances are represented, each 
molecule represents one volume of gas. Hence, every 
equation written in the molecular symbols of aeriform 
substances may be read by volume. For example, 

2H 2 4- 2 = 2H 2 

may be read: Two volumes of hydrogen unite with one 
volume of oxygen to form two volumes of dry steam. 

(a) We give a few examples. 

(1) How much steam is formed by the combustion of 1 liter oil 
hydrogen ? 

Solution. — By referring to the equation just given, we see that 
the volumes of hydrogen and of aeriform H 2 are equal, because it 
shows an equal number of molecules for those substances, and we 
know, from Avogadro's law, that equal numbers of gaseous molecules 
will occupy equal volumes. Hence, the combustion of 1 liter of hydro- 
gen will give 1 liter of dry steam. 

(2) How much oxygen is needed to burn up 500 cu. cm. of 
hydrogen? 

Solution. — The equation for the combustion of hydrogen shows 
that the volume of oxygen is half that of the hydrogen. Hence, it 
will require half of 500 cu. cm. or 250 cu. cm. of oxygen. 

(3) How much hydrogen must be burned to form 4 liters of 
steam ? 

Solution. — The equation shows a relation of equality between the 
volumes of hydrogen and of aeriform H 2 (as in the first example). 
Consequently, 4 liters of steam require 4 liters of hydrogen. 

(4) How much oxygen can be obtained from the electrolysis of 
3 liters of steam ? 

Solution. — The equation shows that the volume of oxygen is half 
that of aeriform H 2 0. Hence, 3 liters of steam will yield 1.5 liters or 
1500 cu. cm. of oxygen. 



140 STOICHIOMETRY, ETC. 

144. Percentage Composition. — Since the symbol of a 
compound represents the number of atoms of each con- 
stituent element of the molecule, and since each atom 
represents a definite weight of that element, the symbol 
of the substance represents both its molecular weight and 
its composition by weight. Thus HN0 3 means that one 
atom of hydrogen, one atom of nitrogen, and three atoms 
of oxygen form a molecule of nitric acid. It also means 
that the molecular weight of nitric acid is sixty-three, the 
sum of the combining weights of the constituent atoms 
(1 -f- 14 -f- 16 x 3). It means, still further, that in sixty- 
three parts by weight of nitric acid, one part is hydrogen, 
fourteen parts are nitrogen, and forty-eight parts are 
oxygen. To find the number of parts of each of these 
constituents in one hundred parts of nitric acid, that is, 
to find the percentage composition of nitric acid, simple 
proportions suffice. 

Solution. — 63 : 1 : : 100 % : 1 .59 %, the proportion of H. 
63 : 14 : : 100 % : 22.22 %, the proportion of N. 
63 : 48 : : 100 % : 76.19 %, the proportion of O. 
100.00% 

Conversely, knowing the percentage composition (which 
may be found by analysis), the molecular weight of the 
substance, and the atomic weights of its constituent ele- 
ments, the chemical formula for the substance may be 
calculated. For instance, the vapor-density of a certain 
compound is fourteen. Analysis shows that eighty-rive 
and seven -tenths per cent of it is oxygen and that fourteen 
and three-tenths per cent of it is hydrogen. What is its 
formula ? 



STOICHIOMETRY, ETC. 141 

Solution. — If its vapor-density is 14, its molecular weight is 28. 

100 % : 85.7 % : : 28 : 24 = C 2 . 

100%: 14.3%:: 28: 4 = H 4 . 

Therefore, the formula is C 2 H 4 . 

Note. — Gaseous volumes will vary with pressure and temperature. 
In comparing such volumes, measured under different conditions, the 
proper correction must be made for this variation. It is common to 
refer gaseous volumes to standard conditions — a temperature of 0°, 
and a pressure of 760 mm. of mercury. The branch of chemistry 
that deals with the numerical relations of atoms is called stoichiometry 
or chemical arithmetic. The gravimetric, volumetric, and percentage 
computations just given are stoichiometrical computations. 

145. Thermochemistry, etc. — Chemical changes are 
generally accompanied by an absorption or an evolution 
of heat. Such thermal changes are directly related to 
changes in the chemical energy (atomic attraction) of the 
substances involved, and conform strictly to the law of the 
conservation of energy (§ 8). 

(a) When in a reaction there is an evolution of heat, as in the 

slacking of lime, 

5 CaO + H 2 = Ca (OH) 2 , 

the loss of chemical energy by the factors is at least equivalent to 
what is called the heat of formation, and the product is less energetic 
than the factors. In other cases, heat is absorbed, the heat of forma- 
tion is negative in value, and the product is more energetic than the 
factors. In the former case, the reaction and the compound are said 
to be exothermic ; in the latter case, both are said to be endothermic. 
The decomposition of an exothermic compound into simpler com- 
pounds or elementary substances is attended with an absorption of 
heat. Similarly, the decomposition of an endothermic compound is 
attended with a liberation of heat. 

(b) The branch of science that includes the various relations 
between chemical action and heat is called thermochemistry. The 
measurement of the heat thus absorbed or evolved has become an 
important part of chemical investigation. 



142 STOICHIOMETRY, ETC. 

(c) The chemical equations described in § 141 ignore the thermal 
changes. Sometimes these are expressed by adding some expression 
more or less definite for the heat of formation, as " + heat " or 
" - 2700 calories." 

(d) In a galvanic cell, part of the chemical energy of the materials 
employed is converted into heat and another part into another form 
of energy that we recognize as an electric current. Whether we 
consider the modern applications of such a current, or the industrial 
applications of steam-power which depends upon the energy of com- 
bustion, or the muscular energy and the heat of animal organisms, 
we are face to face with transformations of energy through chemical 
change. 

EXERCISES. 

1. What do atomic weights express? What weight of oxygen 
may be obtained by decomposing 9 grams of steam? 

2. Give the law of multiple proportions, and illustrate it by the 
compounds of nitrogen and oxygen. 

3. Find the percentage composition of H 2 S0 4 . See the third page 
of the cover of this book. 

4. Marsh-gas is 8 times as heavy as hydrogen. Analysis shows 
that | of its weight is carbon and the rest hydrogen. The atomic 
weight of carbon is 12. What is the formula for marsh-gas? 

5. How much pure zinc is needed to obtain 20 grams of hydrogen? 

6. (a) How much oxygen would be necessary to burn 500 cu. cm. 
of hydrogen ? (Jj) If the experiment was performed in an atmosphere 
at a temperature of 100°, what would be the name and volume of the 
product? (c) How much oxygen would be necessary to burn 5 grams 
of hydrogen? 

7. (a) What liquid is used in the preparation of HC1? (/») What 
is the greatest amount of HC1 that can be prepared by using 196 
grams of that liquid? 

8. (a) What is the difference between hydrochloric acid and 
muriatic acid? (h) What is aqua regia? (c) Name and symbolize 
the five oxides of nitrogen. 

9. (a) Explain the difference between a bivalent and an univa- 
lent metal, (h) What is valence? 

10. When hydriodic acid gas is passed through a heated glass tube, 
it is decomposed, and a violet color appears. Account for the appear- 
ance of the color. 



CHAPTER X. 
NATURAL GROUPS. — THE PERIODIC LAW. 

146. Metallic and Non-metallic Elements. — The ele- 
ments may be separated into two general groups, those 
that form bases when combined with hydrogen and oxy- 
gen, and those that form acids when so combined. Most 
of the base-forming elements are solids with a more or 
less marked metallic luster, and are hence commonly called 
the metallic elements. The acid-forming elements in gen- 
eral have properties opposite to those of the metals. They 
comprise all the gaseous elements except hydrogen which 
does not belong distinctively to either class. 

(a) There is no sharp line between the two classes, each merging 
gradually into the other. Many of the elements thus form hydroxides 
having both acid and basic properties, and several form two oxides 
each, one with basic, and the other with acid-forming tendencies. 

147. Natural Families. — It was early recognized that 
certain of the elements possessed properties that were very 
similar to each other. Shortly after Dalton's hypothesis 
drew attention to the atomic weights, it was seen that 
there- was some sort of relationship between the atomic 
weights of elements that have similar properties. For 
instance, it was shown that in the group of elements, 
chlorine, bromine, and iodine, the properties of which 
show remarkable analogies, the atomic weight of bromine 
is nearly a mean between those of chlorine and iodine. 

143 



144 NATURAL GROUPS. — THE PERIODIC LAW. 

Similar relations were seen in the case of calcium, stron- 
tium, and barium. Arranged in the order of their atomic 
weights, the elements fall easily into groups, the members 
of each group having similar chemical and physical proper- 
ties. Learning the characteristics of these several groups 
and learning to what group any element belongs, one 
thereby learns the most important properties of that ele- 
ment. Such a classification affords a compact simplifica- 
tion of a multitude of facts independently ascertained, and 
is of great aid in systematizing the study of chemistry. 

148. The Periodic Law. — In 1864, Mendeleeff, a Russian, 
and Lothar Meyer, a German, independently announced the 
law that the properties of the elements, both chemical and 
physical, are periodic functions of their atomic weights. This 
means that, if the elements are arranged in the order of their 
atomic weights, at a certain distance beyond any element, 
an element having similar properties will be found. 

(a) On the following page is given a modification of Mendeleeff s 
table. Leaving out hydrogen which, strange to say, hardly finds a 
place in the system, the elements are arranged in the order of their 
atomic weights. Those that fall in any vertical column agree in 
valence and constitute a natural family or group with similar proper- 
ties as above indicated. Read in horizontal lines, the elements con- 
stitute a succession of series. Passing from left to right in any series, 
there is a decrease in the relative quantities of hydrogen with which 
the elements combine, a similar increase in the relative quantities of 
oxygen, and a progressive change from a base-forming to an acid- 
forming nature. The hydroxides of the elements in Group 1 are the 
strongest bases; those of the elements in Group 2 are weaker 
bases ; those of the elements in Group 3 are still weaker ; while those 
of some of the elements in Group 4, instead of having basic prop- 
erties have weak acid properties. Nearly all of the elements 
in Group 5 are acid-forming, while those of Group G and Group 7 
form strong acids. 



Series. 


H N 


W <* 1 »5 » j I* X 


85 C 

H 


H « 


i 


1 g 




II II 

C 3 

il if 


II II 

7 ii 


1 


II II 


I 
1 


t " 


« p? 


ft 


" ii 


n i 


o 

- 1 1 


1 

1 


1 
1 


o 

o 
s 

C 


§ § 


o 


o 

II II 

32 Q 


ii ii 

at c 

32 Jg 


S !l 


i 


1 

00 


| 


S « 


II 
ft 


II ^ 
> 


5 


^ II 

cm 


1 M 


1 


-*' 


§ § 


D 


II "* 


o 
II ° 

o ii 


tH 00 

ll 3 
a II 

02 Cl 


1 
1 


ii § 

jO || 


O 


1 | 


I 


1 II 
32 


II » 

cS II 


CO 

II *J 


1 « 

II 

>< 


p 1 


c 


1 ° 

1 fa 


05 


II "* 
fee II 

o 


K3 i. 


5 =e 

pq 


1 

II 


bo 
~ 1 


o 


>3 


3 


il g» 


II *= 

o ll 


7 3 

to T ~ l 

< II 

6 


T 
i 


ll 
< 

1 


1 




1 
II 


1 1 


1 


1 


i 
i 


1 

1 




2 ? 


3 




»3 «9 


I- * 


s> o 


H N 



SCHOOL CHEMISTRY — 10 



(145) 



146 NATURAL GROUPS. — THE PERIODIC LAW. 

(b) Dropping Groups and 8 from consideration for the moment, 
and passing along Series 2 from Li to F, we find that the nature of 
the element of next higher atomic weight, Na, forces us to return 
from the acid extreme to the basic extreme and to begin another 
series or period. In like manner, after passing along Series 3 from 
Na to CI, we are forced by the nature of K, the element of next 
higher atomic weight, to return to Group 1, and to begin another 
series ; etc. This periodic return being necessary in order to grade 
the properties of the elements according to their atomic weights, the 
result is known as the periodic system of the chemical elements. 

(c) Reference to the table shows that in each group the elements 
are arranged in two columns, each column consisting of the alternate 
elements of that group. These alternate members that thus fall in any 
column show closer grade-relations than do the members of the group 
taken as a whole ; their gradations are quite distinct from those of the 
other column in the same group. So clearly graded in respect to 
their properties are some of the well-known alternate elements of a 
group that they are studied together as a family of elements. In 
other cases, elements next to each other in a series may well be joined 
for study. It is easy to imagine that certain omissions and anomalies 
that pertain to the table (such as putting Na and K into different 
families, and putting Te before I) will disappear with fuller 
knowledge. 

(d) The newly discovered elements related to argon, lacking any 
known valence, appear to constitute a group by themselves. They 
have, therefore, been so placed for convenience of study, and subject to 
further consideration (see § 58). 

(e) Group 8, consisting of three series, each w r ith four elements near 
each other in atomic weight, may be looked upon as lying between 
Group 7 and Group 1. In each there is a return from acid to basic 
nature and from higher to lower valence. The return from Group 8 
to Group 1 is less abrupt than is the return from Group 7. For 
instance, some of the properties of copper, silver, and gold would 
place these elements in Group 8, while other properties would ally 
them to the members of Group 1. Zinc, cadmium, and mercury of 
Group 2 also have properties that relate them to Group 8. These 
relations arising from the divided characters of these six elements 
may be traced more easily if we consider Series 5 as a continuation 
of Series 4 (a long series of 17 members) ; Series 7 as a continuation 
of Series 6: and Series 11 as a continuation of Series 10. 



NATURAL GROUPS. — THE PERIODIC LAW. 147 

( f) An inspection of the table shows that in Group 8 the three 
small groups of four elements each fall in even-numbered series. 
One naturally looks for similar groups in the eighth and twelfth 
series, but they are not yet known. Although in other respects some 
of the series are imperfect, the general arrangement holds good to the 
end. It is not easy to doubt that in some way the properties of the 
elements are determined by their atomic weights. 

(g) When Mendeleeff made his table, scandium, gallium, and 
germanium had not been discovered. From the gap in Group 3, 
Series 4, it was predicted that an element would be found with an 
atomic weight of about 44, and with relations to calcium and titanium 
much like the relations of aluminum to magnesium and silicon. These 
predictions were soon confirmed, the newly discovered scandium fitting 
into the gap and answering with remarkable exactness to the description 
that had been given before it was discovered. Similar predictions were 
fulfilled in similar manner in the cases of gallium and germanium. 
Such verifications constitute almost indubitable evidence of the validity 
of an hypothesis. The gap still existing in Group 7, Series 6, calls for 
an undiscovered, acid-forming element with an atomic weight of about 
100; one that will combine with hydrogen atom for atom, and with 
oxygen in certain definite relations characteristic of the chlorine 
family. 

(/?) The periodic law also stands as the basis of the speculative 
theory that the so-called elements are themselves but combinations of 
a small number of simple elements still unknown to us. 



EXERCISES. 

1. Give the physical and chemical properties of hydrogen. Explain 
the structure of the oxyhydrogen blowpipe. 

2. What chemical process is illustrated in the preparation of 
hydrogen ? 

3. State two ways in which the analysis of water may be effected. 

4. Give the composition of water by volume and by weight. 

5. What is the weight of each constituent in a kilogram of water? 

6. An aeronaut wants 50 kilograms of hydrogen. What substances 
shall he use in making it, and how much of each? 

7. What is meant by atomic weight? 

8. Give the law of multiple proportions. 



148 NATURAL GROUPS. — THE PERIODIC LAW. 

9. What is the difference between air and water, chemically 
considered? 

10. Give one chemical and one physical property of oxygen and of 
am monia. 

11. Write the reactions for the preparation of CI and of HF, and 
state the leading property of each. 

12. When a hot metallic wire is plunged into a certain binary acid 
gas, violet fumes are seen. What is the gas? 

13. How T is chlorine obtained? Explain the reaction. Name the 
most remarkable chemical properties of the substance. 

14. What is the most common compound of chlorine? Find its 
percentage composition. 

15. Give the atomic weight of each of the elements that you have 
studied. 

16. The reaction of chlorine upon ammonia is as follows : 

8XH 3 + 3C1 2 = N 2 + GXH 4 C1. 

(a) What weight of chlorine is necessary to the production of 
12.544 grams of nitrogen ? (b) What volume of chlorine? 

17. Is the combustion of hydrogen an exothermic or an endother- 
mic reaction ? 

18. Determine the percentage composition of a substance that has 
the formula of C 2 H (; 0. 

19. Complete the following equations by inserting the proper 
figures : Mn( ^ + Ha = Mn( -^ + H ^ Q + ^ 

Cu + 8HX0 3 = 2X0 + 3Cu(N0 3 ) 2 4 H 2 0. 

20. (a) Xame three physical properties of oxygen, (b) Two 
chemical properties. (c) How can these chemical properties be 
shown ? (7/) Mention one use of oxygen in the arts. (<?) Explain the 
terms atom and molecule as applied to H 2 0. 

21. (a) If 180 cu. cm. of ammonia are decomposed by electric 
sparks into its elements, what will be the volume of each of these 
elements? (b) If, then, 130 cu. cm. of oxygen are introduced and 
another electric spark is produced in the containing vessel, the tem- 
perature being 16°, what will be the volume of the remaining gaseous 
contents of the vessel ? 



CHAPTER XL 

THE FIRST GROUP 1 — MONADS. 

(The Alkali Metals.) 

Sodium: symbol, Na ; density, 0.97 ; atomic weight, 23; valence, 1. 

149. Occurrence. — Free sodium is not found in nature 
because it unites so readily with oxygen and water, but 
its compounds are very abundant and widely diffused. 
Its most abundant compound is sodium chloride (common 
salt, NaCl), from which, on account of its abundance and 
cheapness, nearly all of the sodium and sodium compounds 
of commerce and science are derived, directly or indirectly. 

(a) Sodium nitrate, carbonate, borate, and silicate, as well as cryo- 
lite, are found in nature. 

150. Preparation. — Sodium was first prepared by the 
electrolysis of sodium hydroxide. Subsequently, it was 
extensively prepared by distilling a mixture of sodium 
carbonate and charcoal. A mixture of common soda-ash 
(Na 3 C0 3 ), coal, and chalk were heated to whiteness in an 
iron cylinder. 

Na 2 C0 8 + C 2 + heat = Na 2 + 3CO. 

1 From this point to the end of the book, the elements will be grouped 
according to the suggestions of the periodic system. Because of the 
anomalous separation of sodium and potassium as mentioned in § 148 (c), 
because hydrogen was considered in an earlier chapter, and because 
copper, silver, and gold, which are related to this group, are to be con- 
sidered as members of Group 8, as suggested in § 148 (e), no attempt will 
be made to divide the members of Group 1 into families. 
149 



150 THE FIRST GROUP — MONADS. 

The escaping sodium vapor was condensed and the carbon 
monoxide was burned. Sodium is now prepared by heat- 
ing an intimate mixture of sodium hydroxide, iron, and 
carbon, or by the electrolysis of caustic soda or of sodium 
nitrate. It must be collected and preserved out of con- 
tact with the air. 

Properties of Sodium. 

Experiment 139. — Wrap a piece of sodium in wire gauze and drop 
it into water. Collect and test the gas evolved. 

Experiment 140. — Fill a test-tube with mercury and invert it over 
that liquid. Thrust a piece of sodium into the mouth of the tube; it 
will rise to the top. Introduce a little water. Explain the resulting 
phenomenon and write the reaction. 

Experiment 141. — Throw a piece of sodium, the size of a pea, on 
cold water. It swims about, decomposing the water, freeing the hy- 
drogen, uniting with the oxygen, and then dissolving in the water. It 
does not evolve enough heat to ignite the hydrogen. 

Experiment 142. — Throw a piece of sodium upon hot 
water, in a large, loosely stoppered bottle. The liberated 
hydrogen is ignited, and gives a yellow, sodium-tinted flame. 

Experiment 143. — Ignite some common alcohol in a 
small saucer. It burns with an almost colorless flame. 
Sprinkle a little common salt into the burning liquid. The 
fig. 46. fl am e becomes yellow. 

Experiment 144. — Wrap a piece of sodium in cloth or in filter-paper 
and place it upon a piece of moist ice. Describe and explain what 
follows. 

151. Properties and Uses. — Sodium is a light metal 
having a brilliant, silver-white luster. It quickly oxi- 
dizes in moist air and decomposes water. It is a good 
conductor of heat and electricity, in which respect it 
ranks next to gold. It is best kept under kerosene or 




THE FIRST GROUP — MONADS. 151 

in a liquid or atmosphere free from oxygen. It is hard 
and brittle at — 20° ; soft like wax at the ordinary 
temperature; semi-fluid at about 50°, and melts below 
the temperature of boiling water. It may be used as a 
reducing agent in the preparation of silicon, boron, mag- 
nesium, aluminum, and most of the metals from their 
oxides. Sodium and all of its compounds impart a yellow 
tinge to flame. 

152. Sodium Oxides, Carbide, and Nitride. — Sodium 
oxide (Na 2 0) has not yet been obtained pure. Sodium 
peroxide (Na 2 2 ) is made by heating sodium in a stream 
of dry air at 300°. It is a yellowish white solid. Sodium 
carbide (Xa 2 C 2 ) with water yields acetylene, and sodium 
nitride (Na 3 N) with water yields ammonia. 

153. Sodium Chloride. — Sodium chloride (common salt, 
NaCl) occurs in immense beds, often hundreds of feet in 
thickness in this country and in Europe. At a depth of 
about a third of a mile, such a bed extends under eastern 
New York and Pennsylvania, northern Ohio, part of 
Michigan, and under Lake Erie into Canada. Salt is 
obtained by mining rock salt when the beds are near the 
surface, or by boring holes and forcing down hot water 
to form a brine, which is pumped out and evaporated, or 
by the evaporation of the saline waters of certain mines, 
springs, and lakes, or of the sea. When the concentrated 
brine is rapidly evaporated by boiling, a fine-grained table 
salt is produced ; when it is evaporated slowly, a coarse 
salt is formed. Sodium chloride crystallizes in cubes, the 
edges of which are sometimes attached so as to form 
hopper-shaped masses. Rock salt is usually found in 




152 THE FIRST GROUP — MONADS. 

cubical crystals, is highly diathermanous and of great 
importance in physical research. The many uses of com- 
mon salt are too familiar to need men- 
tion. One of the most important of these 
is the preservation of meats, in which it 
prevents putrefactive fermentation by 
Fig. 47. destroying the bacteria. 

154. Sodium Sulphate. — Sodium sulphate (salt-cake, 
Na 2 S0 4 ) is prepared in great quantities from salt and 
sulphuric acid. 

(a) The sodium chloride and sulphuric acid are heated in large 
covered pans. The decomposition of XaCl, in the first stage of the 
process, is only partial. 

2XaCl + H 2 S0 4 = NaCl + XaHS0 4 + HCL 

The hydrochloric acid is absorbed in towers filled with coke, over 
which water is kept trickling, and thus becomes a by-product of the 
process. The pasty mass is then strongly heated. 

XaCl + XaHS0 4 = Xa 2 S0 4 + HCL 

The acid is absorbed as in the former stage. 

(b) The Xa 2 S0 4 dissolves easily in warm water. When such a 
concentrated solution cools, 10 molecules of water are taken up to 
form Glauber's salt (Xa.,S0 4 , 10 H 2 0). Many salts owe their crystal- 
line form to the presence of a definite quantity of water that may be 
driven off by heat — the so-called "water of crystallization." Ex- 
posed to dry air, the Glauber's salt crystals effloresce (i.e., give up 
their water of crystallization), and are changed to Xa 2 S0 4 . 

(c) Sodium -hydrogen sulphate (XaIIS0 4 ) is often called sodium 
disulphate, or bisulphate of soda. 

Sodium Carbonate. 

Experiment 145. — Expose a piece of freshly cut sodium weighing 
about half a gram on a watch-glass, and note during several days the 
changes that follow. The metal quickly tarnishes, becomes coated 



THE FIRST GROUP — MONADS. 153 

with the white hydroxide, and is moistened by the water it absorbs 

from the air. 

2Xa, + 2 = 2Xa 2 0, 

Xa 2 + H 2 = 2XaOH. 

As above indicated, both the oxide and the hydroxide are deliques- 
cent. The absorption of water will continue until the whole mass 
becomes liquid. The liquid then absorbs carbon dioxide from the 
air, and the resulting carbonate unites with the water present to form 
soda crystals. 

2XaOH + C0 2 = Na 2 C0 3 + H 2 0, 

Na 2 C0 3 + 10H 2 O = Xa 2 C0 3 , 10H,O. 

These crystals in turn effloresce and fall to a white powder of partly 
dehydrated soda. 

155. Sodium Carbonate. — Sodium carbonate (soda, 
Na 2 C0 3 ) is made in immense quantities from common 
salt by the Leblanc process, so called from the name of 
its inventor. 

(«) The first step is the preparation of the salt-cake, as described 
in the last paragraph. The Xa 2 S0 4 is then heated in a reverberatory 
furnace with an equal weight of calcium carbonate (chalk or lime- 
stone, CaCOo), and about half its weight of coal. The resulting 
product, called black-ash, is essentially a mixture of sodium car- 
bonate and calcium sulphide. 

Xa 2 S0 4 + 4C = Na 2 S + ICO. 

Xa 2 S + CaC0 3 = Na 2 C0 3 + CaS. 

Although the changes may be considered as taking place in succes- 
sion, as above indicated, in the actual process the two reactions take 
place simultaneously. The calcium sulphide thus produced is not 
readily soluble in water, as is the Na 2 C0 3 . When the black-ash is 
lixiviated with water, and the solution is evaporated to dryness and 
calcined, the result is soda-ash, the common name of the commercial 
article. The sulphur of the CaS is recovered and made into sul- 
phuric acid. This process was invented in France at the time of the 
French revolution, when the supply that had formerly come from the 
ashes of sea-plants was cut off. 



151 THE FIRST GROUP — MONADS. 

(b) Although large quantities of the soda are still made in this 
way, the process is now carried on largely on account of what was 
formerly a by-product and a nuisance — the hydrochloric acid. This 
acid is utilized in the manufacture of chlorine for bleaching-powder. 
When processes for making chlorine directly from chlorides are per- 
fected, the Leblanc process will give way for the cheaper Solvay, or 
ammonia-soda, process. 

156. The Ammonia Process. — The Solvay process 
depends upon the fact that when a solution of sodium 
chloride is mixed with a solution of ammonium-hydrogen 
carbonate, the less soluble sodium-hydrogen carbonate is 
formed and separates from the solution of ammonium 
chloride. KaC1 + XH j IC03 = XaHC0 3 + NH 4 CL 

In practice, a saturated salt-brine is treated in tanks with 
gaseous ammonia until the solution is saturated. After 
cooling, the liquid is pumped to the top of a steel tower 
about six feet in diameter and about fifty feet high. In 
the tower are perforated iron plates at intervals of about 
three feet, and so arranged that the descending liquid is 
brought into intimate contact with the ascending gases. 
Carbon dioxide is pumped in at the bottom of the tower, 
and under pressure sufficient to force it up through the 
descending solution of salt and ammonia. As the liquid 
and the gas come into contact, sodium-hydrogen carbonate 
is formed, ready for separation at the bottom of the tower. 

NaCl + NH 3 + C0 2 + H 2 = NaHC0 3 + NH 4 C1. 
The ammonium-chloride solution thus formed is treated 
with slacked lime (calcium hydroxide). 

2NH 4 C1 + Ca(OH) 2 = 2NH 3 + CaCl 2 + 11,0. 
The gaseous ammonia thus recovered is again used for 
the saturation of brine. The calcium chloride is a waste 






THE FIRST GROUP — MONADS. 155 

product of the process. The carbon dioxide used is sup- 
plied by the burning of limestone (CaC0 3 ) in kilns. 

CaC0 3 + heat = C0 2 + CaO. 

The quicklime (CaO) so made is slacked to the hydroxide 
and used for the recovery of the ammonia, as above indi- 
cated. Thus, the substances consumed are salt, lime- 
stone, and the coal used to evolve the necessary heat ; 
the exit-products are sodium-hydrogen carbonate and 
calcium chloride, the latter being of no present value. 
By gently heating the sodium -hydrogen carbonate, it is 
converted into sodium carbonate and carbon dioxide. 

2NaHC0 3 + heat = Na 2 C0 3 + C0 2 + H 2 0. 

The gas thus produced is returned to the carbonating 
tower. 

(a) No soda has ever been made in this country by the Leblanc 
process, but very large Solvay soda plants are located at Syracuse, 
New York ; Detroit, Michigan ; and Barberton, Ohio. 

(b) By dissolving soda-ash in hot water and allowing the solu- 
tion to cool and stand for several days, large transparent crystals of 
"washing-soda" (soda-crystals, sal-soda, Na 2 C0 3 , 10 H 2 0) are formed. 
These crystals part with their water of crystallization by efflorescence 
or heating. The dry residue is Na 2 C0 3 purified by the process of 
crystallization, one of the most valuable known means of purification. 

157. Sodium-hydrogen Carbonate. — Sodium-hydrogen 
carbonate (soda, baking-soda, sodium bicarbonate, NaHC0 3 ) 
is easily prepared by passing a stream of carbon dioxide 
through a solution of sodium carbonate or by exposing 
soda-crystals to an atmosphere of carbon dioxide. 

Na 2 C0 3 + H 2 + C0 2 = 2NaHC0 3 

or Na 2 C0 3 , 10 H 2 + C0 2 = 2NaHC0 3 + 9 H 2 0. 



156 THE FIRST GROUP — MONADS. 

Sodium bicarbonate is used in medicine, in cooking, in 
the manufacture of baking-powders and of carbon dioxide, 
and for many purposes where a mild alkali is needed. 

Note. — In common speech, the word soda is applied both to sodium 
carbonate and to sodium-hydrogen carbonate. It is even used as a 
synonym for sodium hydroxide. 

158. Baking-powders. — These are mixtures of sodium 
bicarbonate with some acid or acid salt, capable of setting 
the carbon dioxide free from the former when the mixture 
is wet. To prevent the reaction from taking place pre- 
maturely, some inert substance like flour or starch is added 
to the mixture to keep it as dry as possible. The acids and 
the acid salts most generally used are tartaric acid, potas- 
sium acid tartrate or cream of tartar (see § 299), calcium 
acid phosphate (see § 353, <?), and alum (see § 217). With 
tartaric acid or with cream of tartar, a neutral tartrate of 
sodium or of sodium and potassium is formed, and is left 
in the baked bread or biscuit. When calcium acid phos- 
phate is used, the residue is calcium phosphate and sodium 
phosphate. When alum is used, the residual products 
of the reaction are potassium and sodium sulphates and 
aluminum hydroxide. This aluminum hydroxide has an 
astringent action when it is dissolved, for which reason 
alum powders are objected to by many persons. One 
of the products in each of the above reactions is carbon 
dioxide, the evolution of which causes the bread to be- 
come light. Hence, the baking-powder is valuable in 
proportion to the amount of this gas given off under 
the conditions of baking, provided the residual products 
are harmless. 



THE FIRST GROUP — MONADS. 157 

159. Sodium Hydroxide. — Sodium hydroxide (caustic 
soda, sodium hydrate, NaOH) is formed when sodium is 
thrown upon water, but in practice it is made from sodium 
carbonate by treating its solution with lime, or by the 
electrolysis of common salt. It is a white, opaque, brittle 
solid of fibrous texture. It deliquesces in the air, absorb- 
ing moisture and carbon dioxide, and changing thus to the 
non-deliquescent carbonate the coating of which protects 
the hydroxide from further loss. It is a strong base, a 
powerful cautery, and is largely used in the laboratory 
and in various industrial processes. An impure variety is 
known as "concentrated lye." 

(a) Crude Na 2 C(X is dissolved in boiling water. Cream of lime is 
added until the hot solution is free from C0 2 . 

NavjCOg + Ca(OH) 2 = 2XaOH + CaC0 3 . 

The insoluble CaC0 3 is removed from the solution of XaOH by 
precipitation and nitration. The XaOH is then evaporated until an 
oily liquid is obtained. This liquid solidifies on cooling. The purified 
product is usually cast in the form of sticks. 

(b) Caustic soda is made in large quantities as an incidental prod- 
uct of the manufacture of Na 2 CO a , being cheaply prepared from the 
liquor from which the black-ash is deposited. 

• Experiment 146. — Make a strong solution of caustic soda and put it 
into a retort or a flask with some granulated zinc. Heat the flask over 
a sand-bath or wire gauze until the liquid boils. A gas will be evolved. 
Collect it over water and find out what it is. 



EXERCISES. 

1. Write the formula for decahydrated sodium sulphate. 

2. Write the formula for anhydrous sodium carbonate. 

3. What is the formula for sodium chloride ? 

4. Write the graphic formula for the disulphate of soda. 



158 THE FIRST GROUP — MONADS. 

5. The sodium obtained in practice being one- third the theoretical 
yield, what weight of the metal can be prepared from 159 kilograms 
of sodium carbonate? 

6. What is the percentage composition of NaN0 3 ? 

7. What weight of KC10 3 is needed to furnish enough oxygen to 
burn the hydrogen evolved by the action of 200 grams of sodium upon 
water ? 

8. (a) Find the weight of 1 liter of each of the following : N, 
COo, O, CH 4 . (b) Find the volume of 1 gram of each. 

9. Write the name and full graphic formula for 

(HO) - (S0 2 ) - S - (S0 2 ) - (HO). 

10. Why is sulphuric acid said to be dibasic? 

11. Name some monobasic acid. Name some tribasic acid. 

12. What is the difference between a normal salt and an acid 
salt ? 

13. How many tons of soda-ash will result from the calcination of 
fifty tons of sodium-hydrogen carbonate? 

14. How much sodium hydroxide can be made from 1000 grams of 
sodium carbonate? How much calcium hydroxide will be required? 
How much calcium carbonate will be formed ? 



Potassium : symbol, K ; density, 0.875 ; atomic weight, 39 ; valence, 1. 

160. Source. — Potassium compounds are found widely 
distributed in nature, forming an essential constituent of 
many rocks and of all fruitful soils. These compounds 
are taken from the soil by the rootlets of plants, none of 
which can live without them. It is essential to animal 
life also. Free potassium is not found in nature. 

161. Preparation. — Potassium is generally prepared by 
heating intensely a mixture of its carbonate with charcoal. 

K 2 C0 3 + C 2 =K 2 + 3CO. 

It is also prepared by the electrolysis of its hydroxide. 



THE FIRST GROUP — MONADS. 



159 




Properties of Potassium. 

Experiment 147. — Drop a piece of potassium, half the size of a pea, 
upon water. It decomposes the water, the 
hydrogen burns with a flame beautifully violet 
tinted, with the vapor of potassium. If the 
water is in an open dish, stand at a distance 
of a meter or more, as the combustion will 
terminate with a slight explosion. Test the 
water at the end of the experiment with red- 
dened litmus-paper. Fig. 48. 

Experiment 148. — Stretch a piece of blotting-paper upon a wooden 
tray, wet the paper with a red solution of litmus and throw upon it a 
small piece of sodium or of potassium. The track of the metal as it 
runs over the moistened paper will be written in blue lines, showing 
the formation of an alkaline product. 

Experiment 149. — Hold a small piece of potassium under water by 
means of a wire gauze or filter-paper. Collect the gas evolved as 
shown in the figure. What is this gas ? 




Experiment 150. —In Fig. 50, a represents a bottle for the genera- 
tion of carbon dioxide ; c, a drying-tube containing calcium chloride ; 
e, a tube of Bohemian (hard) glass with a delivery-tube, t, dipping 



160 



THE FIRST GROUP — MOXADS. 



into the bottle, i. When a lighted match thrust into i is quickly 
extinguished, we may know that the apparatus is filled with carbon 
dioxide. Then, dry a piece of potassium the size of a pea by pressing 
it between folds of filter- or blotting-paper, remove t, thrust the 
potassium into e, and replace t. When the potassium is heated by the 




lamp-flame it will burn, taking oxygen from the carbon dioxide and 
depositing black carbon upon the walls of e. 

2K 2 + 3C0 2 = 2K 2 C0 3 +C. 

The particles of black carbon may be made more evident by placing 
e in a bottle of clear water, to dissolve the K 2 C0 3 . 

Experiment 151. — Repeat Experiment 150, using a current of hy- 
drochloric acid instead of carbon dioxide. Collect over water the gas 
delivered through t. What is this gas ? Write the reaction. 

Experiment 152. — Repeat Experiment 151, using ammonia instead 
of HC1. Write the reaction. 

Experiment 153. — Bore a half-inch hole two inches deep in a block 
of ice. Enlarge the bottom of the cavity to the size of a hickory nut. 
Into this cavity, drop a piece of potassium, the size of a pea, and notice 
the beautiful volcanic action. Make the experiment in a warm and 
darkened room. 



162. Properties. — Potassium is a light metal having a 
brilliant bluish white luster. In electropositive character- 
istics, it ranks third among the metals, and in lightness, 



THE FIRST GROUP — MONADS. 161 

second. It is brittle at zero ; soft like wax at 15°, 
and easily welded when the surfaces are clean ; it melts 
at about 63°. Its physical and chemical properties 
closely resemble those of sodium, but it is less used on 
account of its greater cost. Like sodium, it is best kept 
under petroleum. Its salts communicate a violet tint to 
flame. 

(a) Potassium forms two oxides, K 2 and K 2 2 . 

163. Potassium Chloride. — Potassium chloride (KC1) is 
found in sea-water and other salt waters, and is largely 
prepared from the mother-liquor from which the sodium 
chloride has crystallized, and from the Stassfurt deposit 
of carnallite (KC1, MgCl 2 , G H 2 0). It resembles sodium 
chloride in appearance and taste but is more easily soluble 
in water. It dissolves in about three times its weight of 
water at the ordinary temperature, producing great cold. 
Like sodium chloride, it crystallizes in cubes. Potassium 
chloride is largely used in the manufacture of potassium 
hydroxide, and as a source of potassium in fertilizers. 

(a) The other potassium halogen salts, potassium bromide, potas- 
sium iodide, and potassium fluoride also crystallize in cubes, have a 
saline taste, and easily dissolve in water. Potassium bromide and 
potassium iodide are used in medicine and in photography. 

164. Potassium Cyanide. — Potassium cyanide (KCN or 
KCy) is a white, fusible, deliquescent and intensely poi- 
sonous solid. It is used in photography and as a labora- 
tory reagent. It is a powerful reducing agent. As its 
solution dissolves silver and gold cyanides, it is largely 
used in electroplating, and in the extraction of gold and 
silver from their ores. 

SCHOOL CHEMISTRY 11 



162 THE FIRST GROUP — MONADS. 

Caution. — Potassium cyanide is poisonous not only when taken 
internally, but also when brought into contact with an abrasion of the 
skin, a cut, or a scratch. Its best antidote is the inhalation of chlo- 
rine, which may be quickly prepared from bleaching-powder, and the 
inhalation of ammonia as a stimulant. Cold douches and artificial 
respiration may also be helpful, but the action of the poison is usu- 
ally too quick for the successful application of the remedy. 

165. Potassium Carbonate. — Potassium carbonate 
(K 2 C0 3 ) is generally prepared in this country by leach- 
ing wood- ashes to form potash -lye and evaporating the lye 
in large pots or kettles, whence the name of the crude 
article, potash. The potash, when refined, is called pearl- 
ash. A pure carbonate, prepared by igniting the bicar- 
bonate, is called salt of tartar. Potassium carbonate is a 
deliquescent salt with a .strong alkaline taste and reaction. 

(a) Potassium carbonate was formerly of more importance than 
n.ow, as the Leblanc and the Solvay processes have rendered sodium 
carbonate so much cheaper that it has largely replaced the former in 
commerce and the arts. As K 2 C0 3 is hygroscopic and Xa 2 C0 3 is not, 
the latter is much more convenient for storing and handling. 

(b) As Xa 2 C0 3 is used in making hard soap, so K 2 C0 3 is used in 
making soft soap. 

(c) The rapid extinction of American forests has greatly checked 
the manufacture of American potash. Similar causes have operated 
in Europe. Hence, other sources have been sought and large quanti- 
ties are now made from the refuse material of the beet-root sugar 
manufacture and also from K 2 S0 4 by a process similar to the Leblanc 
process for preparing Xa 2 C0 3 . 

166. Potassium-hydrogen Carbonate. — Potassium-hydro- 
gen carbonate (saleratus, potassium bicarbonate, KHC0 3 ) 
is prepared by passing a current of carbon dioxide through 
a strong solution of potassium carbonate. 

K 2 C0 3 -f- ILO + CO„ = 2KIICO-. 



THE FIRST GROUP — MONADS. 163 

The pure, crystalline potassium bicarbonate is used in 
medicine. The somewhat impure quality known as sale- 
ratus was formerly used extensively in cooking, but its 
place has been almost completely taken by the better and 
cheaper sodium bicarbonate, which is sometimes called 
soda saleratus. 

167. Potassium Hydroxide. — Potassium hydroxide 
(caustic potash, potassium hydrate, KOH) may be pre- 
pared from potassium carbonate as sodium hydroxide is 
from sodium carbonate. Its physical and chemical prop- 
erties closely resemble those of sodium hydroxide. It 
combines with fats and oils to form soft soap, and is one 
of the strongest bases known. 

(«) As KOH absorbs water and carbon dioxide from the air, it is 
gradually changed to K 2 CO s . As this salt is deliquescent, the change 
goes on until all of the KOH is changed to a syrup of K 2 C0 3 . Conse- 
quently, it should be kept in closely stoppered bottles. It is usually 
cast in the form of sticks. 

(&) Caustic potash is easily but not cheaply prepared by the action 
of potassium upon water. 

(<?) A solution of caustic potash quickly destroys both animal and 
vegetable substances. It is best clarified by subsidence and decan- 
tation, though it may be filtered through glass, sand, asbestos, or 
guncotton. 

Experiment 154. — Repeat Experiment 146, using KOH instead of 
XaOH. 

168. Potassium Nitrate. — Potassium nitrate (niter, 
saltpeter, KX0 3 ) is found as an efflorescence on the soil 
in various tropical regions, especially in Bengal. It does 
not extend into the soil to a depth greater than that to 
which the air can easily penetrate. It is extracted by 
solution in water and evaporation. It is also found in 



164 THE FIRST GROUP — MONADS. 

many caverns, and is seldom wanting in a fruitful soil. 
It is chiefly used in the preparation of nitric acid and the 
manufacture of gunpowder. It is a white, inodorous 
solid, permanent in the air and very soluble in hot water. 

(a) "When animal or vegetable matter decays in the presence of air 
and in contact with an alkaline or earthy base, the NH 3 produced is 
gradually oxidized to HNG 3 and " fixed " by the alkali. Thus the 
well-waters of most towns contain nitrates, showing that they have 
been contaminated by sewers, cesspools, or other causes. The artifi- 
cial production of potassium nitrate is regularly carried on in Sweden, 
Switzerland, and other parts of continental Europe. 

Lithium: symbol, Li; density, 0.59; atomic weight, 7 ; valence, 1. 

169. Lithium. — This element is the lightest known 
solid. It is a rare, silver- white metal with a grayish 
tinge. It is ductile and malleable, harder than sodium 
or potassium and softer than lead. It melts at about 
180°. In appearance and chemical properties, it is similar 
to sodium and potassium, but it is less violent in its reac- 
tions. For example, it decomposes water, but not with 
combustion of the hydrogen or ignition of the metal. It 
was first prepared in the metallic state in 1855. 

Rubidium : symbol, Rb ; density, 1.52 ; atomic weight, 85 ; valence, 1. 

170. Rubidium. — This is a rare, lustrous, silver-white 
metal with a tinge of yellow. It resembles potassium so 
closely that it can be distinguished from it only by spec- 
troscopic analysis, the most delicate of determinative pro- 
cesses. It was discovered by this means in 1861. It 
melts at a temperature of 38.5°, and at —10° is as soft 
as wax. It oxidizes rapidly in the air with the evolution 
of much heat that results in ignition. It does not keep 



THE FIRST GROUP — MONADS. 165 

well under petroleum, and is best preserved in hydrogen. 
Excepting caesium, it is the most strongly electropositive 
of the metals. Like the other alkali metals, it does not 
occur free in nature. 

Cesium : symbol, Cs ; density, 1.88; atomic weight, 132 ; valence, 1. 

171. Caesium. — This is a ductile, silver- white metal, 
very soft at ordinary temperatures. It closely resembles 
potassium and rubidium, with which it usually occurs. 
It melts at a temperature of 27°. It burns rapidly when 
heated in air, and takes fire when thrown on water. It 
may be kept under petroleum. It is the most decidedly 
electropositive of the metals. It was discovered by the 
spectroscope in 1860, the first element so discovered ; its 
detection still requires the spectroscope. 

172. Ammonium. — As stated in § 62 (&), ammonium is 
a name given to the compound radical, NH 4 . It acts, as 
do the other members of this group, as an alkaline monad 
metal, but it has not been isolated. 

(a) The assuming of this hypothetical metal makes the analogies 
between the composition of the salts of the " volatile alkali " and the 
composition of those of the fixed alkalies as evident as are the analo- 
gies between their properties ; e.g., 

Ammonium hydroxide. Potassium hydroxide. Sod ivm hydroxide. 

S H 4o sio *; a io. 



H \ Hj" H 

173. Ammonium Chloride. — Ammonium chloride (sal- 
ammoniac, NH 4 C1) is found native in certain volcanic 
regions, and is artificially prepared in large quantities 
from the ammomacal liquors of gas-works. It occurs in 
commerce as tough, fibrous masses. It is used in medi- 



166 THE FIRST GROUP — MONADS. 

cine, in soldering to dissolve the metallic oxides, in dye- 
ing, and in the laboratory as a convenient source of 
ammonia and for other purposes. 

(a) The ammoniacal liquor of gas-works is heated with lime and 
the gaseous ammonia thus evolved is passed through dilute hydro- 
chloric acid until it is saturated. The solution is evaporated and the 
NH 4 C1 purified by recrystallization from hot water or by sublimation. 

Experiment 155. — Dissolve 6 grams of ammonium nitrate in 10 
cu. cm. of ice-cold water. Stir the mixture with a thermometer and 
notice the resulting temperature. 

174. Ammonium Nitrate. — Ammonium nitrate (XH 4 
N0 3 ) is prepared by neutralizing dilute nitric acid with 
dilute ammonia-water or a solution of ammonium car- 
bonate and evaporating the solution. It decomposes by 
heat into water and nitrogen monoxide. It has a saline 
taste, and dissolves easily in half its weight of water with 
the absorption of heat. 

Note. — Ammonium salts are very numerous, most of them being 
prepared directly or indirectly from the ammoniacal liquors of gas- 
works. They are generally soluble in water. 

EXERCISES. 

1. The practical yield being half the theoretical, how much potas- 
sium may be prepared from 138,080 grams of potassium carbonate? 

2. Wh at is the percentage composition of KC10 3 ? Of KX0 3 ? 

3. What is the object of having the room warm for Experi- 
ment 153? 

4. Give at least one reason in favor of each of the following 
formulas for sal-ammoniac: NH 8 HC1 and NH 4 C1. 

5. Complete the following equations : 

(a) IIXO, + NH 3 = 
(h) H,S() 4 + 2KOH = 
(c) 2IIX0 3 + PbO = 



THE FIRST GROUP — MONADS. 167 

6. What is the molecular weight of caustic potash? 

7. I explode a mixture of 4 liters of hydrogen and 5 liters of 
chlorine. (a) What volume of HC1 is produced? (b) Which of the 
original gases and how much of it remains uncombined? 

8. What volume of N 2 may be formed by heating 30 grams of 
NH 4 X0 3 ? 

9. Assuming that water will absorb half its weight of ammonia, 
calculate the amount of NH 4 C1 necessary to the production of 3 kilo- 
grams of NH 4 HO. 

10. The name and formula for potassium cyanide suggest a com- 
pound radical. Consult the index of this book and hunt up references 
that look " promising " until you find the name of that compound 
radical. Then write the graphic formula for potassium cyanide and 
determine the valence of each of the three elements and of the com- 
pound radical. 

11. Name two chemical properties of hydrogen that are the reverse 
of two of oxygen. 

12. («) How is nitric acid prepared on a large scale? (b) How 
can you show that an acid is an acid? (c) What are alkalis? 
(Y/) What is "laughing-gas"? 

13. («) What are bases? (b) What class of elements forms 
acids? (c) What class of elements forms bases? (d) W^hat is a 
salt? 

14. (a) What is the combining weight of a chemical compound? 
(6) HNO s + KHO = KNO3 + H 2 0. What is the relative amount of 
the substances used ? 



CHAPTER XII. 
THE SECOND GROUP — DYADS. 

I. THE CALCIUM FAMILY. 
Beryllium: symbol, Be; density, 1.85; atomic weight, 9; valence, 2. 

175. Beryllium. — This rare element is also known as 
glucinum (Gl). It is a silver- white, malleable, and 
strongly electropositive metal. It generally occurs as a 
silicate with aluminum, and in its general properties, 
stands between the other alkaline earth metals and alumi- 
num. Its oxide is found in the mineral beryl from which 
it was first discovered. It is prepared by heating its 
chloride (BeCl 2 ) with sodium in a closed iron crucible, or 
by heating its oxide (BeO) with magnesium. 

Calcium : symbol, Ca. ; density, 1.6 to 1.8 ; atomic weight, 40 ; valence. 2. 

176. Calcium. — Calcium compounds occur largely dif- 
fused in nature, especially the carbonate in the forms of 
calcite, chalk, marble, limestone, coral, etc. They are 
found in all animal and vegetable bodies. The metal was 
first obtained by Davy, in 1808, by the electrolysis of its 
chloride. It has recently been prepared by the electroly- 
sis of fused calcium iodide (Cal 2 ), and also by heating a 
mixture of calcium iodide and sodium in a closed crucible. 

Cal 2 4- Na a = Ca 4- 2NaI. 

168 



THE CALCIUM FAMILY. 



169 



Calcium is a yellowish-white, soft, ductile, and malleable 
metal. It is scarcely oxidizable in dry air, is easily oxi- 
dizable in moist air, burns vividly with a very bright 
yellow light when heated to redness in the air, and decom- 
poses water with evolution of hydrogen. 

177. Calcium Oxides, etc. — Calcium monoxide (lime, 
quicklime, CaO) is prepared by heating calcium carbonate. 
In some parts of ^, 

the country, it is 
"burned" from 
limestone (CaC0 3 ) 
in a kiln of rude 
masonry often built 
in the side of a hill, 
the process requir- 
ing several days, and 
a temperature of 
400° or more. 

(a) In such a kiln, a 
limestone arch is built 
above the fire and the 
remaining limestone 
placed upon this arch 
from above. When the lime has been burned, the kiln is allowed to 
cool, the CaO is removed, and a new charge is introduced. This 
requires the cooling of the furnace for each lot burned. In most 
places, the process is continuous, the limestone and coal or coke 
being fed in at the top of a shaft furnace from the bottom of which 
the CaO is removed while still hot. These kilns are similar in shape 
to the blast-furnaces used in making pig-iron. They are about 50 ft. 
high, 6 to 8 ft. in diameter, made of heavy iron plate on the outside, 
and lined with fire-brick. In many places, the C0 2 expelled from 
the limestone is absorbed and used, as in the manufacture of soda 
and of sugar. 




Fig. 51. 



170 THE SECOND GROUP — DYADS. 

(b) Calcium dioxide (Ca0 2 ) has been prepared by precipitation 
from lime-water with H 2 2 . 

(c) Calcium hydride (CaII 2 ), calcium carbide (CaC 2 ), and calcium 
nitride (Ca 3 X 2 ) decompose water on contact. 

CaH 2 + 2II 2 = Ca (OH) 2 + 2H 2 . 
Ca 3 N 2 + 6II 2 = 3Ca (OH) 2 + 2NH 3 , 

Calcium carbide is made on the large scale by heating a mixture of 
lime and charcoal to the intense temperature made available by the 
electric furnace. It is a comparatively cheap commercial article. Its 
reaction with water yields acetylene gas (see § 2G4). 

178. Properties, Uses, etc. — Lime is a white, amorphous 
substance about three times as heavy as water. It is 
infusible in the oxyhydrogen flame, and when so heated 
emits an intense light known as the lime or calcium light 
(see Experiment 46). It fuses and volatilizes at the tem- 
perature of the electric arc. It is largely used in making 
mortars and cements, in the manufacture of sugar, in the 
Solvay process for making soda, and in the Clark method 
of softening hard water (§ 184, a), in the preparation of 
sodium hydroxide, in many industries where a cheap 
alkali is needed for neutralizing acids, and, in the labora- 
tory, for drying gases and liquids, and for other purposes. 

(a) When CaO is exposed to the air, it absorbs water and carbon 
dioxide and falls to a powder known as air-slacked lime — a mixture 
of calcium hydroxide (Ca0 2 H 2 ) and calcium carbonate (CaC0 3 ). 

179. Calcium Chloride. — Calcium chloride (CaCl 2 ) is 
easily prepared by the action of hydrochloric acid upon 
marble, and the evaporation of the solution. It lias a 
strong attraction for water, is deliquescent, and is used 
for drying gases. 



THE CALCIUM FAMILY. 171 

(a) Calcium chloride may be crystallized from a saturated solution. 
These crystals (CaCl„, 6 H 2 0), when mixed with snow, produce a 
temperature of — -48°. 

Caustic Lime. 

Experiment 156. — Add a few drops of water to a small quantity of 
slacked CaO, and rub it to a paste between the fingers. It has a 
slightly caustic effect, dissolving the surface of the cuticle. 

Experiment 157. — Put 30 grams of recently burned CaO upon a 
saucer, hold the saucer in the palm of the hand, and pour 20 cu. cm. 
of water upon it. Notice the increase of bulk and the rise of tempera- 
ture. Thrust a friction match into the crumbling mass. It will be 
heated to the point of ignition. Sprinkle a little gunpowder upon 
the slacking lime ; perhaps it will take fire. 

180. Calcium Hydroxide. — When fresh, well-burned 
lime is treated with one-third its weight of water, the 
direct synthesis yields calcium hydroxide [calcium 
hydrate, caustic lime, slacked lime, Ca(OH) 2 ] with the 
evolution of great heat. Calcium hydroxide is a white, 
alkaline, caustic powder. It dissolves more easily in cold 
than in hot water, yielding an alkaline, feebly caustic 
liquid called lime-water. Lime-water readily absorbs 
carbon dioxide. Lime-water containing solid particles 
of calcium hydroxide in suspension is called milk of 
lime, or cream of lime, according to the consistency of 
the mixture. 

(«) The power of absorbing carbon dioxide and hydrogen sulphide 
leads to the use of Ca(OH) 2 in the purifiers of gas-works. Its caustic 
action leads to its use (as milk of lime) in removing the hair from 
hides for tanning. Large quantities are used in the preparation of 
mortar, and for absorbing chlorine in the manufacture of bleaching- 
powder. 

(/>) Slacked lime mixed with water and sand makes a mortar that 
hardens or sets in the air but not in water. This mortar slowly absorbs 
carbon dioxide from the air and becomes a mixture of calcium hydrox- 



172 THE SECOND GROUP — DYADS. 

ide, calcium carbonate, and sand. The burning of a limestone that 
contains more than about 15 per cent of siliceous clay (aluminum 
silicate) yields "hydraulic" lime. Such lime is used in making hy- 
draulic mortar or cement, which sets or hardens even under water 
(see § 327, i). The theory of the hydraulicity of cement is not clearly 
understood. 

Calcium Carbonate. 

Experiment 158. — Place a little lime-water in a test-tube and pass 
through it a stream of C0 2 . Notice the precipitation of CaC0 3 that 
renders the liquid turbid. Notice also that as the passage of C0 2 into 
the liquid continues, the latter becomes clear again, the precipitate 
being dissolved. Boil the clear liquid to expel some of the absorbed 
dioxide, and the precipitate again appears. Test the liquid at each step 
of the experiment with litmus-paper to determine whether it gives an 
acid or an alkaline reaction. 

181. Calcium Carbonate. — Calcium carbonate (CaC0 3 ) 
occurs in many forms, both crystallized and amorphous. 
The shells of oysters, clams, and other mollusks are almost 
wholly calcium carbonate. It forms the greater part of 
egg-shells and of bones. As marble and limestone, it is 
found in immense masses. It is barely soluble in water. 
Water charged with carbon dioxide dissolves it more easily, 
forming calcium bicarbonate. 

CaC0 3 + H 2 C0 3 = CaH 2 (C0 3 ) 2 . 
When such waters are exposed to the air, they lose part 
of their carbon dioxide and, consequently, precipitate the 
calcium carbonate previously" held in solution. Hence, the 
formation of stalactites, stalagmites, tufa, travertine, etc. 
As carbon dioxide is present in many natural waters, caves 
are often formed by them in limestone rocks. All the 
forms of calcium carbonate are easily acted upon by even 
dilute acids, the action being attended by effervescence 
due to the escape of the expelled carbon dioxide. 






THE CALCIUM FAMILY. 173 

(a) Limestone is used in immense quantities as a building-stone, 
as a flux in smelting many ores, in the manufacture of quicklime and 
Portland cement (§ 327, i), and in the preparation of carbon dioxide. 

182. Calcium Sulphate. — Calcium sulphate (CaS0 4 ) is 
found in nature as the mineral anhydrite. The hydrated 
sulphate (CaS0 4 , 2H 2 0) is the mineral gypsum, which, 
when in the crystalline form, is called selenite. By heat- 
ing gypsum to about 120° it parts with its water of crys- 
tallization forming plaster of Paris. When this plaster is 
mixed to a paste with water, it again unites with the water 
and hardens or "sets" with increase of volume. Hence, 
its use as a cement and for making casts of various objects. 
Calcium sulphate is sparingly soluble in water. 

183. Calcium Phosphate. — There are several calcium 
phosphates, the most important of which is bone-phosphate, 
Ca 3 (P0 4 ) 2 . It is the chief inorganic constituent of the 
bones of animals. It is important as a source of phos- 
phorus, and, when ground to a powder and treated with 
acid, is valuable as a fertilizer. 

Hard Water. 

Experiment 159. — Dissolve about half a gram of calcium chloride 
in about 200 cu. cm. of water, and add a slight excess of ammonium 
carbonate. Calcium carbonate will be precipitated. Allow it to 
settle, decant the solution, and wash the precipitate once or twice by 
decantation. Add about 200 cu. cm. of cold water to the washed pre- 
cipitate and pass in a slow current of carbon dioxide, shaking often, 
until the precipitate dissolves. To a third of this solution, add lime- 
water a little at a time until no more precipitate is formed on standing 
for several minutes. Boil another third of the solution until about a 
quarter of it has been evaporated. In each case, test the precipitate 
formed for calcium carbonate. To the remaining third of the solution, 
add a solution of soap and notice that a lather can not be produced 
until all the calcium salt is removed. 



174 THE SECOND GROUP — DYADS. 

184. Hard Water. — Natural waters that contain cal- 
cium or magnesium salts in solution are called hard, 
because vegetables do not soften so readily when boiled 
in them as they do when boiled in pure water. Such 
waters are ill-fitted for many industrial purposes, espe- 
cially for use in steam-boilers or for washing. These 
salts are generally bicarbonates, sulphates, or chlorides. 
Boiling such a water results in the decomposition of the 
bicarbonates, the formation of carbon dioxide and the less 
soluble carbonates. 

CaH 2 (C0 3 ) 2 = CaC0 3 + C0 2 + H 2 0. 

This reaction also takes place very slowly when the water 
is exposed to the air. For these reasons, such hardness 
caused by bicarbonates is called " temporary hardness," 
while that due to sulphates and chlorides is called u per- 
manent hardness." 

Calcium sulphate is less soluble in water at high than 
at low temperatures. The bicarbonates and the calcium 
sulphate are precipitated from solution when heated in 
steam-boilers, the precipitate usually forming a hard and 
tenacious coating on the boiler-flues. As these compounds 
are poor conductors of heat, a boiler so coated is wasteful 
of fuel. The scale often becomes so thick that the fuel 
necessary for the generation of steam is- doubled. Vari- 
ous substances are used to prevent such precipitated salts 
from adhering to the boiler, but, when possible, it is better 
to remove the cause of the hardness before the water is 
put into the boiler. 

(«) Clark's method of softening water that is hard by reason of the 
presence of bicarbonates consists in adding lime-water. The calcium 



THE CALCIUM FAMILY. 175 

hydroxide combines with half the carbon dioxide of the bicarbonates, 
thus forming carbonates that are precipitated. 

CaH 2 (C0 3 ) 2 + Ca(OH) 3 = 2CaC0 3 + 2H 2 0. 

Of course, just the right quantity of lime-water must be used. If too 
little of the lime-water is added, the water will remain hard ; if too 
much is added, the softened water will be made hard by the excess. 
The quantity of lime-water used is determined by analysis of the hard 
water to be treated. 

In like manner, calcium and magnesium sulphates may be removed 
by adding a solution of sodium carbonate which precipitates the car- 
bonates of calcium and magnesium respectively. 

CaS0 4 + Na 2 C0 3 = CaC0 3 + Na,S0 4 . 

After adding the precipitating reagents, the water is allowed to stand 
until the carbonates have settled. As the sodium sulphate is not 
precipitated, it forms no scale. 

(b) Hard waters react with soap to form insoluble calcium or mag- 
nesium soaps that rise to the surface as a curdy scum. In such waters, 
soap must be added until these insoluble salts are precipitated before 
a lather can be formed or any washing value obtained from the soap 
used. Hence, for washing purposes, hard waters are not economical. 

185. Strontium and Barium. — These rare metals re- 
semble calcium in appearance and properties. The mineral 
strontianite is strontium carbonate ; the mineral celestine 
is strontium sulphate. The mineral witherite is barium 
carbonate ; heavy spar is barium sulphate. 

(a) The relations of these metals to calcium sufficiently appear in 
the formulas of some of their compounds : 



CaO 


Ca0 2 


CaC0 3 


CaS0 4 


SrO 


Sr0 2 


SrC0 3 


SrS0 4 


BaO 


Ba0 2 


BaC0 3 


BaS0 4 



186. Erbium. — This is a metallic element found along 
with yttrium, terbium, etc., in gadolinite and other rare 
minerals. Erbium metal has not yet been prepared. 



176 THE SECOND GROUP — DYADS. 

187. Radium, etc. — To the calcium family belongs the 
element radium, typical of a class of substances known as 
radioactive. This term is applied to substances that pos- 
sess the power of spontaneously and continuously emitting 
rays that are capable of passing through substances opaque 
to ordinary light, of darkening a photographic plate, and 
of rapidly discharging an electroscope. The discovery of 
this phenomenon was made in 1896 by Henri Becquerel 
while investigating certain uranium compounds. These 
rays are, therefore, sometimes known as Becquerel rays. 
Although not visible in themselves, they cause many sub- 
stances to become visibly luminous. An X-ray screen in 
a darkened room is made faintly luminous by the very 
close presence of a small quantity of a pure salt of radium. 
Thorium and uranium appear to be feebly radioactive, but 
the three recently discovered elements — radium, polonium, 
and actinium — possess the power in a remarkable degree. 
Radium has a high atomic weight and some properties in 
common with those of barium. It has been produced only 
in minute quantities. Its chief source has been uraninite 
or pitchblende (see § 373). Some of its salts, especially 
radium bromide and radium chloride, which in appearance 
much resemble common salt, have been obtained in minute 
quantities. The pure metal is very unstable ; so easily 
oxidizable that its preparation and preservation have, so 
far, been practically impossible. Polonium and actinium 
have so far been found only in quantities insufficient for 
their isolation in a pure state. Theoretically considered, 
these three are very interesting elements, and may serve 
to advance our knowledge of the constitution of matter, 
and of the structure of the atoms themselves. 



THE CALCIUM FAMILY. 177 

(a) The radium radiations appear to be of three distinct kinds, 
designated respectively as a (alpha), j3 (beta), and y (gamma) rays. 
The a-rays have a slight power of penetrating opaque substances 
and can be deflected by a magnet. The /3-rays have a considerable 
power of penetrating opaque substances, produce phosphorescence in 
many substances, and can be deflected by a magnet. In many respects, 
they are similar to the cathode rays produced by an electric discharge 
in a vacuum tube. The y-rays have a remarkably high penetrating 
power, and are not deflected by a magnet ; they are thus similar to 
Roentgen or X-rays. 

(b) The explanation of the phenomena of radium can not be con- 
sidered as satisfactorily established. The disintegration theory has 
been more vigorously advanced than any other. According to this 
theory, the a-rays consist of streams of positively electrified bodies, 
approximately the size of hydrogen atoms, and moving with a velocity 
of about 20,000 miles a second. Because of this enormous velocity, 
these particles have an energy so great that their impacts on a zinc- 
sulphide screen produce a faint light, and are microscopically visible as 
separate starlike flashes. Each colliding particle, however, is so minute, 
that there is no perceptible loss of weight in the radioactive substance 
itself. Most of the particles projected from the interior portion of such 
a substance are intercepted before they leave the radiating mass; for 
this reason pure radium is always a few degrees warmer than its sur- 
roundings, the impacts of the arrested particles generating heat. In 
like manner, the /3-rays are supposed to consist of streams of nega- 
tively charged particles of almost inconceivable minuteness, approxi- 
mating a thousandth part of the mass of a hydrogen atom, and moving 
with a velocity of about that of light. The y-rays are not electrically 
charged, and therefore can not be deflected by a magnet, 

EXERCISES. 

1. Write the reaction for the burning of lime. 

2. Write the reaction for the preparation of CaCI 2 . 

3. Write the reaction for preparing calcium hydroxide. 

4. Why is the formula for calcium hypochlorite CaCl 2 2 instead of 
CaCIO, the formula for hypochlorous acid being HCIO ? 

5. When a current of carbon dioxide is passed through an aque- 
ous solution of Ba0 2 , hydroxyl and BaCO s are formed. Write the 
reaction. 

SCHOOL CHEMISTRY — 12 



178 THE SECOND GROUP — DYADS. 

6. How much potassium nitrate and sulphuric acid shall I need to 
prepare enough nitric acid to neutralize 5 kilograms of chalk? 

7. What is the property that chiefly distinguishes chlorine and the 
elements most like it from potassium and the elements most like it? 

8. Write the graphic formula for a compound radical that acts as 
an alkaline, monad metal. 

9. What are the characteristic properties of chlorine? 

10. Write the graphic formulas for common salt, caustic potash, 
and manganese dioxide. 

11. Is the reaction involved in the slacking of quicklime endother- 
mic or exothermic ? 

12. Compare and contrast chlorine and iodine, respecting their 
physical and chemical properties. 

13. What is the difference between potassium nitrate and Chile 
saltpeter? 

11. What is the lightest known metal ? 

15. What is the weight of a cubic decimeter of quicklime? 

16. Is calcium chloride a solid or a liquid? Give a reason for your 
answer based upon some statement in this section of this chapter. 

17. Explain the formation of a stalactite. 

18. What kind of hard water may be softened by the addition of 
caustic lime? Explain the process. 

19. Sometimes the inner surfaces of boiler-flues have to be scraped 
clean. Explain the cause of such a necessity. 

20. Why is it more easy to cleanse greasy hands with rain-water 
than with hard water ? 



H. THE ZINC FAMILY, 

Magnesium ; symbol, Mg ; density, 1.75; atomic weight, 21 , 
valence, 2. 

188. Magnesium. — Magnesium compounds are widely 
and abundantly distributed but the metal is not found 
free in nature. The metal is prepared in considerable quan- 
tities by fusing together magnesium chloride (MgCl 2 ) and 
sodium or potassium, by electrolysis of the chloride or 
sulphate, and in other ways. It has a silver- white appear- 



THE ZINC FAMILY. 179 

ance, is malleable and ductile, preserves its luster in dry 
air, and tarnishes in moist air. It is readily acted upon 
by most acids with the evolution of hydrogen and, as it 
is perfectly free from arsenic, is often used, instead of 
zinc, in Marsh's test for arsenic. It is found in commerce, 
usually in the form of ribbon. This ribbon, when ignited, 
burns with a brilliant light of high actinic power. 

Magnesia. 

Experiment 160. — Coil 15 cm. of magnesium ribbon around a lead 
pencil. Change the pencil for a knitting-needle or an iron wire, hold 
the wire horizontal, and ignite one end of the ribbon. The coil^ of 
magnesium will burn to an imperfect coil of magnesium oxide. 

189. Magnesium Oxide. — Magnesium oxide (magnesia, 
MgO) is formed when the metal is burned in air. It is 
generally prepared by the ignition of magnesium carbon- 
ate. It is used for making crucibles and furnace-linings, 
as it does not melt below the temperature of the oxyhy- 
drogen flame. It is also used in medicine. 

190. Magnesium Salts. — Magnesium chloride (MgCl 2 ) 
is found in sea-water, in many saline springs, and as a 
constituent of carnallite. It is largely used, in dressing 
cotton goods. Magnesium sulphate (MgS0 4 ) is found in 
nature as kieserite. The hydrated salt (MgS0 4 , 7 H 2 0) 
is called Epsom salt, and is found in many mineral waters. 
It is used in medicine and in dressing cotton goods. Mag- 
nesium carbonate (MgC0 3 ) occurs as native magnesite. A 
mixture of the carbonate and the hydroxide [Mg(OH) 2 ], 
prepared by adding sodium carbonate (Na 2 C0 3 ) to a solu- 
tion of magnesium chloride or of Epsom salt, is called 
magnesia alba. 



180 



THE SECOND GKOUP — DYADS. 



Zinc : symbol, Zn ; density, 7.14 ; atomic weight, G5 ; valence, 2. 

191. Sources of Zinc. — Metallic zinc is not found in 
nature. The carbonate (smithsonite, zinc spar, Zn.C0 3 ), 
the silicate (calamine, Zn 2 Si0 4 ), the sulphide (sphalerite, 
blende, ZnS), and the oxide (red zinc ore, zincite, ZnO) 
are found as minerals and used as ores of zinc. 

192. Preparation. — The zinc ore is first roasted and 
thereby converted to an oxide. This oxide is then heated 

in clay retorts with half 
its weight of coal. The 
carbon of the coal takes 
the oxygen from the zinc 
oxide, reducing the latter 
to a metal which distills 
and is condensed in re- 
The zinc, when melted and 




Fig. 52. 

ceivers outside the furnace. 



cast into cakes, is called spelter. 

(a) Zinc and mercury are the only common metals that are vapor- 
ized easily enough to be distilled and purified in this way. The clay 
retorts from which the zinc is distilled are arranged in rows in a 
furnace where they are heated white-hot by coal or gaseous fuel. 

Experiment 161. — Dissolve 10 grams of lead acetate (sugar of lead) 
in 250 cu. cm. of water and add a few drops of acetic 
acid. In this solution, suspend a strip of zinc. The 
zinc and the lead will change places, leaving a solution 
of zinc acetate and a metallic "lead tree." The tree 
will be more beautiful if the ends of the zinc are slit 
into branches before immersion. The weights of the 
dissolved zinc and the precipitated lead will be in the 
ratio of their atomic weights. Fig. 53. 

193. Properties. — Zinc is a bluish white, crystalline 
metal. It is ductile and malleable at about 130° or 140°, 




THE ZING FAMILY. 181 

under which circumstances it may be drawn into wire, or 
rolled into sheets Or plates. At the ordinary temperature 
and at temperatures above 200°, it is so brittle that it may 
be easily powdered in a mortar. The commercial article 
is seldom pure, generally containing lead, iron, and carbon, 
while traces of arsenic and antimony are often found. 
Metallic zinc in the form of fine dust and mixed with zinc 
oxide is obtained in considerable quantities in the manu- 
facture of the metal. This mixture, technically known as 
zinc-dust, is a valuable reducing agent. Zinc is readily 
acted upon by a boiling solution of sodium and potassium 
hydroxides and by most acids, with the evolution of 
hydrogen. It melts at about 418°, and distills at about 
1000°. Pure zinc is not easily soluble in dilute sulphuric 
acid while impure zinc is thus soluble. Zinc is not much 
affected by air, either dry or moist. It readily precipitates 
most metals from solutions of their salts. 

(a) Brass is an alloy of zinc and copper. German silver is an 
alloy of zinc, copper, and nickel. 

(6) Galvanized iron is simply iron coated with zinc. The term 
is a misnomer, as galvanic action is not involved in the process. 

194. Zinc Compounds. — The mineral zincite, an impure 
zinc oxide, is found as an ore in New Jersey. Its color is 
due to the presence of red oxide of manganese. Pure 
zinc oxide (ZnO) is known in commerce as zinc white, 
and is prepared on a large scale for use as a paint. Zinc 
chloride (ZnCl 2 ) is formed by dissolving zinc in hydro- 
chloric acid. It is used for preserving timber, as a caustic 
in surgery, in cleansing the surfaces of metals for soldering 
and, very largely, for the fraudulent purpose of weighting 
cotton goods. It is soluble in alcohol and very deliques- 



182 THE SECOND GROUP — DYADS. 

cent. Zinc sulphate (white vitriol, ZnS0 4 , 7 H 2 0) is 
used in medicine, in dyeing, and in galvanic batteries. 

Cadmium : symbol, Cd ; density, 8.6 ; atomic weight, 112 ; valence, 2. 

195. Cadmium. — This rare metal occurs in nature asso- 
ciated with zinc ores. As it is more volatile than zinc, its 
vapor comes over with the first portion of the zinc distilled. 
It forms compounds very similar to the corresponding zinc 
compounds. It has a tin-white color, is susceptible of a 
high polish, and gives a crackling sound when bent, as tin 
does. As its vapor-density is about 56, we conclude that 
its molecule contains but a single atom (§ 136, «). 

Mercurv: symbol, Hg ; density, 13.6 ; atomic weight, 199; valence, 1, 2. 

196. Source. — Mercury, or quicksilver, is found native 
in small quantities, but chiefly as a sulphide (HgS) called 
cinnabar. The best known deposits of cinnabar are at 
Idria in Austria, Almaden in Spain, and New Almaden 
in California. Mercury is also brought from the Ural, 
China, and Japan. 

197. Preparation. — Sometimes the ore is roasted with 
a lvgulated supply of air. 

HgS + 2 = Hg + S0 2 . 

The sulphide is generally mixed with quicklime or iron- 
scale or turnings, and distilled. The sulphur unites with 
the lime or the iron, and the mercury vapor is condensed 
by being brought into contact with water. 

4HgS + 4CaO = 3CaS + CaS0 4 + 4IIg. 



THE ZINC FAMILY. 183 

198. Properties. — Mercury is a silver-white metal, the 
only metal that is liquid at the ordinary temperature. It 
vaporizes slowly at ordinary temperatures, and boils at a 
temperature of about 357°. It freezes at a temperature 
of about — 39°, becoming a ductile, malleable, white solid 
that can be cut with a knife. At a very low temperature 
it becomes hard and brittle. It is a good conductor of 
electricity. The liquid metal is hardly affected by expos- 
ure to the air but, when heated for a long time in the air, 
it oxidizes. It is soluble in strong, boiling sulphuric acid, 
but its best solvent is nitric acid. As its vapor-density 
is about 100, we conclude that its molecule contains but 
a single atom (§ 136, a). 

199. Uses. — Mercury is largely used in the construc- 
tion of thermometers, barometers, and other physical and 
chemical apparatus, for the collection of gases that are 
soluble in water, for the preparation of mirrors, for the 
extraction of gold and silver from their ores, and for the 
preparation of various mercurial compounds. 

Amalgams. 

Experiment 162. — Prepare an amalgam by adding bits of sodium 
to mercury slightly warmed in an evaporating-dish. 

200. Amalgams. — Compounds or mixtures of the 
metals with mercury are called amalgams. They are 
generally formed by the direct union of the two metals. 
Many of these amalgams, or mercury alloys, are largely 
used in the arts. Tin amalgam is used in " silvering " 
mirrors ; silver and tin amalgam gradually hardens and 
is used for filling teeth; zinc and tin amalgam is used 
for coating the rubbers of electric machines. 



184 THE SECOND GROUP — DYADS. 

201. Mercury Oxides. — Mercury forms two oxides, 
mercurous oxide (suboxide of mercury, gray oxide of 
mercury, Hg 2 0) and mercuric oxide (red oxide of mer- 
cury, red precipitate, HgO). The latter is a powerful 
poison. It is prepared by heating mercury for a long 
time in air or, on the large scale, by heating an intimate 
mixture of mercury and mercuric nitrate. It decom- 
poses, at a red heat, into its elementary constituents 
(see Experiment 29). 

202. Mercury Sulphide. — This compound (HgS) is 
largely found native as cinnabar. When prepared arti- 
ficially, it is called vermilion. It is of a brilliant red 
color, and is used as an oil and water-color paint, in 
lithographers' and printers' inks, and in coloring sealing- 
wax. 

Mercury Salts. 

Experiment 163. — Place a drop of a solution of mercurous nitrate 
or of corrosive sublimate upon a clean copper coin. Rub the drop 
over the coin and mercury will be deposited upon the copper. 

203. Mercury Salts. — Mercury forms two series of 
salts, corresponding to the two oxides, the mercurous salts 
and the mercuric salts. The members of the two series 
are widely different in their properties. The mercuric 
compounds are very much more poisonous than are the 
mercurous. 

(a) Mercury may be detected in almost any of its salts by placing 
a piece of clean copper in a solution of the salt. 

204. Mercurous Salts. — The most important mercurous 
salt is mercurous chloride (calomel, HgCl). It is taste- 
less, odorless, and insoluble in water, and is largely used 



THE ZINC FAMILY. 185 

in medicine. It is commonly prepared by sublimation 
from an intimate mixture of mercury and mercuric 
chloride. 

(a) Mercurous nitrate (HgN0 3 ) is formed by the action of cold, 
dilute nitric acid on mercury. Mercurous sulphate (Hg 2 S0 4 ) is formed 
by heating concentrated sulphuric acid with an excess of mercury or 
by precipitating HgN0 3 with sulphuric acid. 

(b) Mercurous bromide (HgBr) may be precipitated by adding 
hydrogen bromide or potassium bromide to a solution of HgN0 3 . 
Similarly, mercurous iodide (Hgl) may be precipitated by adding 
potassium iodide to a solution of HgN0 3 . It is also formed when 
iodine is rubbed with the right proportion of mercury, a small quan- 
tity of alcohol being added. It is a green powder and gradually 
decomposes into HgT 2 and Hg. 

205. Mercuric Salts. — Mercuric chloride (corrosive 
sublimate, HgCl 2 ) is a powerful poison. It coagulates 
albumen, forming an insoluble compound, in consequence 
of which the white of eggs furnishes the best antidote in 
case of poisoning by this salt. It unites with many other 
organic substances to form insoluble, stable compounds. 
It is somewhat soluble in cold water and easily soluble in 
hot water. It is prepared by subliming a mixture of 
mercuric sulphate and sodiam chloride. It is one of the 
most efficient germicides known and is therefore used as 
an antiseptic and for preserving animal and vegetable 
tissues from decay. 

(a) Botanical and zoological specimens are preserved from decay 
and from the attacks of insects by brushing over them a solution of 
HgCl 2 in alcohol. 

(b) Mercuric nitrate [Hg(N"0 3 ) 2 ] is prepared by boiling mercury 
in nitric acid until a portion of the liquid no longer gives a precipitate 
with common salt. Mercuric sulphate (HgSOJ is prepared by heating 
mercury with at least one and a half times its weight of sulphuric acid. 



186 THE SECOND GROUP — DYADS. 

(c) Mercury combines directly with bromine forming mercuric 
bromide (HgBr 2 ), and evolving heat. When mercury is rubbed in a 
mortar with iodine and a small quantity of alcohol, it forms mercuric 
iodide (Hgl 2 ), and evolves heat. Mercuric iodide may be precipitated 
by adding potassium iodide to a solution of HgCl 2 . It is a scarlet 
powder (see Experiment 10). 

EXERCISES. 

1. In the preparation of magnesium from magnesium chloride and 
sodium, what is the other product of the reaction? How may it be 
separated from the metal ? 

2. How much ZnO can be obtained by oxidizing 100 grams of zinc ? 

3. If 150 cu. cm. of oxygen and 400 cu. cm. of hydrogen are mixed 
and exploded, what volume of steam is produced? Which gas and 
how much of it remains in excess? 

4. By a series of electric sparks, I decompose 100 cu. cm. of NH y 
I then add 90 cu. cm. of oxygen, and explode the mixture. Give the 
name and volume of each of the remaining gases. 

5. Name an element that is thought to be monatomic, and give a 
reason for such belief. 

6. A certain salt absorbs water from the air and then dissolves in 
the water. What word describes the salt in this respect ? 

7. Complete and read aloud the following equations : 

Na + H,0 = XaHO 
CaO + H 2 = 

8. An old process of preparing HgCl was to sublime a mixture 
that gave this reaction : HgS0 4 + Hg + 2NaCl = Na 2 S0 4 + 2HgCl. 
Write this equation in full molecular symbols. 

9. Is cinnabar a mercurous or a mercuric compound? 

10. How many pounds of mercury may be obtained from a ton of 
pure cinnabar? 



CHAPTER XIII. 

THE THIRD GROUP — TRIADS. 

I. THE BORON FAMILY. 

Boron : symbol, B ; density, 2.45 (amorphous) to 2.68 (crystalline) ; 
atomic weight, 11 ; valence, 3. 

206. Boron. — This element is not found free in nature. 

It is prepared by heating its oxide with sodium or with 

aluminum, by electrolysis, and in other ways. In the 

crystalline form, it is nearly as hard, lustrous, and highly 

refractive as the diamond. It may also be prepared as 

an amorphous, soft brown powder, or in scales with a 

graphite-like luster. It has one oxide (boron trioxide, 

boric or boracic anhydride, B 2 3 ). Its most important 

compound is borax (sodium pyroborate, Na 2 B 4 7 ), large 

quantities of which are found in California. 

(a) It forms BCL,, BF 3 , BH 3 , and BBr 3 . In the heat of an electric 
furnace, it unites with carbon to form boron carbide. This carbide is 
similar to carborundum (silicon carbide), but even harder. 

Boric Acid. 

Experiment 164. — Dissolve 6 grams of powdered borax in 15 or 20 
cu. cm. of boiling water. Add 3 or 4 cu. cm. of hydrochloric acid or 
2 cu. cm. of sulphuric acid ; stir and allow to cool. Crystals of boric 
acid will be formed. 

Experiment 165. — Heat some boric acid crystals in a clean iron 

spoon. The heated crystals first melt, and then become viscous as the 

water is driven off. Touch this mass with a glass rod and draw out 

the adhering mass into long threads. This viscous substance is B 2 3 . 

187 



188 



THE THIRD GROUP — TRIADS. 



207. Boric Acids. 




Fig. 54. 



Boric acid (H 3 B0 3 ) is a white, 
crystalline, lustrous solid 
that may be freed from any 
borate by the action of almost 
any other acid,in consequence 
of which it is considered a 
very feeble acid. It may be 
formed by the union of the 
oxide with water. Upon 
fusion, it gives up this water, 
forming a glassy mass of 
boric anhydride. Large 
quantities of boric acid are 
used as a preservative for 
milk and canned meats and 
vegetables. 

(a) In addition to the boric (or 
orthoboric) acid above mentioned, 
two other acids may be formed by 
the union of boron oxide with 
water, as follows: 

B 2 3 + 3H 2 = 2H 3 B0 3 , 
boric or orthoboric acid. 

B 2 3 + H 2 = 2HB02, 
metaboric acid. 

2B 2 0., + H 2 = H 2 B 4 7 , 
tetraboric or pyroboric acid. 

(h) Native boric acid is found 
free in the volcanic regions of 
Tuscany whence nearly all that is 
brought into commerce is obtained. 
Volcanic jets of steam, charged 
with HgBOg, issue into natural or 



THE BORON FAMILY. 189 

artificial ponds or lagoons, the water of which condenses the steam 
and becomes charged with the acid. Upon evaporation, these waters 
yield pearly crystals of H 3 B0 3 . 

Test for Boric Acid. 

Experiment 166. — Dissolve a few crystals of H 3 B0 3 in alcohol. 
Upon igniting the alcohol and stirring the solution, the flame will be 
of a beautiful green color ; or add a little alcohol and sulphuric acid 
to a solution of borax. Heat the materials and ignite the vapor ; the 
flame will be tipped with green. 

Experiment 167. — To a very dilute solution of borax add a few 
drops of hydrochloric acid and, with the solution, moisten a strip of 
turmeric-paper, i.e., filter-paper colored with a solution of turmeric. 
Upon drying the paper, its color changes to a bright pink. 

208. Tests. — The color that boric acid imparts to an 
alcohol-flame, and the color that it yields with turmeric- 
paper afford the most convenient tests for its presence. 
The turmeric test enables the detection of boric acid in 
the ash of food products that have been adulterated 

with it. 

Borax. 

Experiment 168. — Make a small loop at the end of a platinum 
wire, the other end of which has been fused into a piece of glass tub- 
ing for a handle. Heat the loop red-hot, touch it to some powdered 
borax, and heat the borax that adheres to the loop, thus forming a 
clear, glassy bead. Into this bead fuse a minute particle of some 
cobalt compound, closely observing it, until a transparent blue glass 
is formed. If too much of the cobalt compound is added, the glass 
will be opaque. After observing the color of the bead when cold and 
when heated in different parts of the blowpipe-flame, dip the hot bead 
quickly into water, and clean the wire. Repeat the experiment with 
a compound of copper, with one of chromium, and with manganese 
dioxide. 

209. Borax. — Borax (sodium pyroborate, Na 2 B 4 7 , 
10H 2 O), is found in certain lakes of India, China, Per- 



190 THE THIRD GROUP — TRIADS. 

sia, Ceylon, Peru, and Bolivia. Large quantities are 
obtained from Borax Lake, California, and from Pyramid 
Lake, Nevada, by evaporating the water and purifying the 
separated borax by crystallization. When heated, it intu- 
mesces and loses the water of crystallization, finally fusing 
to a clear glass. Fused borax dissolves many metallic 
oxides, forming colored glass-like substances. Hence 
it is extensively used in the glazing of porcelain, in 
porcelain paints, in some kinds of glass and enamels, 
and for freeing metal surfaces from oxides preparatory 
to soldering. 

210. Rare Elements of the Boron Family. — The other 
elements of this family, scandium, yttrium, lanthanum, 
and ytterbium, are rare metals, so rare that they need 
little more than mention here. Their properties are suffi- 
ciently indicated by their grouping (see tables in Chap- 
ter X., and Appendix, § 1). As already stated, the exist- 
ence and properties of scandium were predicted by the aid 
of the periodic law. 

EXERCISES. 

1. What is the molecular weight of boron trioxide? 

2. What per cent of boron is there in orthoboric acid? 

3. Write the formula for calcium (Ca") pyroborate ; for boric 
anhydride. 

4. What is the basicity of H 3 B0 3 ? 

5. (a) Write the symbols for the most common oxygen and 
hydrogen compounds with elements of the chlorine group. (/>) Give 
the valence of each element, (c) State the gradation of physical and 
chemical properties among these elements, (d) Give easy tests for 
chlorine and iodine. 

6. Write the equation for the reaction involved in Experiment 
165. 



THE ALUMINUM FAMILY. 191 

7. By strongly heating manganese dioxide it is reduced to a 
lower oxide, thus : 

3Mn0 2 = Mn 3 4 + 0. 2 . 

What weight and what volume of oxygen can be thus prepared from 
50 grams of Mn0 2 ? 

8. State the method of preparing nitric acid and the amount of 
each substance needed for 10 pounds of the acid. 

9. How does a chloride differ from a chlorate ? Illustrate by 
potassium compounds. 

10. What is the weight of the chlorine* in 5 pounds of common 
salt ? What per cent of oxygen is there in potassium chlorate ? 

11. State the economic properties of chlorine, and show on what 
they depend. 

12. Name two of the most useful compounds of nitric acid, with 
some use of each. 

13. The formula for acetylene is C 2 H 2 . Acetylene and benzene 
have the same percentage composition, but the former has a vapor- 
density of 13, and the latter a vapor-density of 39. From these data 
determine the formula for benzene. 



H. THE ALUMINUM FAMILY. 
Aluminum: symbol, Al ; density, 2.6; atomic weight, 27 ; valence, 3. 

211. Source. — Aluminum ranks third among the ele- 
ments and first among the metals in quantity and extent 
of distribution. It is not found native ; its oxide is found 
in the minerals emery and corundum, among the purer 
varieties of which are the ruby and the sapphire ; its 
fluoride, in cryolite ; its silicates, in the feldspars and 
micas, the disintegration of which, by weathering, gives 
rise to the several kinds of clay. It is also found in the 
topaz, emerald, and garnet. It constitutes about one- 
twelfth of the earth's crust, and is contained in all fertile 
soils, but is not taken up by any plants except a few 
cryptogams. 



192 THE THIRD GROUP — TRIADS. 

212. Preparation. — Aluminum was first obtained by 
Wohler, in 1827, by heating aluminum chloride with 
sodium. It was first prepared on a commercial scale by 
St. Claire-Deville, in 1856, by reducing sodium-aluminum 
chloride by sodium. 

A1C1 3 , NaCl + 3Na = 4NaCl + Al. 

The price of the metal made by this method never fell 
much below that of silver. At present, it is prepared by 
electrolyziug a solution of aluminum oxide in a bath o.f 
molten cryolite. The principal works are at Niagara 
Falls, and at Shaffhausen in Switzerland. This method 
of production has so reduced the price of the metal that 
aluminum competes with copper and other metals for 
man/ uses. A great many methods have been patented. 

213. Properties. — Aluminum is a remarkably light and 
sonorous metal. It is of a bluish- white color and suscep- 
tible of a bright polish. It is tenacious, and very malle- 
able and ductile. It is about as hard as silver and melts 
at about 655°. It is best worked at a temperature of 
from 100° to 150°. It does not readily oxidize in air. 
At ordinary temperatures, it is soluble in nitric and sul- 
phuric acids. Its best solvents are hydrochloric acid and 
boiling solutions of the alkali hydroxides. 

214. Uses. — The lightness, luster, strength, unaltera- 
bility in air and in hydrogen sulphide, ease of working, 
sonorous and non-poisonous qualities of aluminum adapt 
it for many uses. It is used in large quantities for elec- 
trical conductors, for light castings and sheet-metal, for 
boats, canteens, cooking utensils, and for making delicate 



THE ALUMINUM FAMILY. 193 

balances, light weights, opera glasses, and physical, surgi- 
cal, and other instruments calling especially for lightness 
and moderate strength. Aluminum bronze (ninety per 
cent copper plus ten per cent aluminum) is very hard and 
malleable, } r ields fine castings, has the tenacity of steel and 
the color of gold, and takes a high polish. 

215. Aluminum Oxide. — Aluminum oxide (alumina, 
A1 2 3 ) occurs native in corundum, ruby, sapphire, etc. 
Its crystals are second in hardness only to the diamond. 
Small artificial rubies and sapphires, having all the prop- 
erties of the natural crj^stals, have been made. An impure 
granular variety is called emery. 

Aluminum Hydroxide. 

Experiment i6g. — To a solution of common alum in water, add 
ammonia-water or ammonium sulphide until a gelatinous mass is 
formed. This mass is aluminum hydroxide. 

216. Aluminum Hydroxide. — Aluminum hydroxide 
[Al(OH) 3 ] is largely used as a mordant in dyeing textile 
fabrics. In crystallized form, it occurs in nature as hydrar- 
gillite. It is soluble in acids and in alkalis. In one case 
it acts like a base; in the other, like an acid. See § 148 (a). 
The salts thus formed with the alkalis are called alumi- 
nates, the alkali metal replacing the hydrogen of the 
hydroxyl, thus Al(OK) 3 or Al(ONa) 3 . 

217. Alums. — Common alum is a double sulphate of 
aluminum and potassium [A1K(S0 4 ) 2 , 12H 2 0]. Ammo- 
nium alum or sodium alum differs in composition by hav- 
ing ammonium or sodium in place of the potassium. 

SCHOOL CHEMISTRY 13 



194 THE THIRD GROUP TRIADS. 

218. Other Aluminum Compounds. — Cryolite is a double 
fluoride of aluminum and sodium. A deposit eighty feet 
thick and three hundred feet long is known on the west 
coast of Greenland. But the most important of the alu- 
minum compounds are the silicates, some of which have 
been mentioned. One of the most important constituents 
of the great rock masses of the earth is feldspar, a double 
silicate of aluminum and potassium (AlKSi 3 8 ). Exposed 
to the weather, feldspar undergoes a natural decomposi- 
tion. The soluble potassium salts thus formed are 
washed out and find their way into the soil. The 
insoluble aluminum silicate is carried down the sides 
of the hills and mountains upon which it was formed 
into the valleys and streams. The purest form of this 
natural product is called kaolin ; the impure varieties 
constitute ordinary clay. The color of the clay is largely 
determined by the presence of iron hydroxides. 

(a) When kaolin is mixed with feldspar, or some other flux, and 
melted, it forms a translucent substance called porcelain. Ordinary 
clay is largely used in the production of earthenware, which, like the 
porcelain products, may be glazed or unglazed. The most common 
variety of unglazed earthenware is bricks, the color of which is largely 
due to the presence of iron oxides. 

219. Rare Elements of the Aluminum Family. — Gallium, 
indium, and thallium are rare metals that were discovered 
by the spectroscope in the latter half of the nineteenth 
centur}^. The existence of gallium had been predicted 
by the aid of the periodic law. Thallium forms two 
oxides, the monoxide (T1 2 0) and the trioxide, or sesqui- 
oxide (T1 2 3 ). There are two corresponding series of 
salts, the thallious and the thallic. 



THE ALUMINUM FAMILY. 195 

Note. — The atomic weights assigned to the unclassified elements, 
gadolinium, samarium, terbium, and thulium, indicate that some of 
them have properties not widely different from those that charac- 
terize this group. In fact, some authorities count samarium and 
terbium (as well as erbium) as triads. 

EXERCISES. 

1. Which of the metals mentioned in this chapter is of the greatest 
industrial importance ? 

2. (a) How many cu. cm. of oxygen may be obtained by the 
electrolysis of 10 grams of water? (7;) How many of hydrogen? 

3. How many pounds of aluminum might be made by the complete 
electrolysis of a ton of pure aluminum oxide? 

4. Write the formula for the oxide of gallium. 

5. The symbol for water was formerly written HO and (for some 
years subsequently) H 2 2 . What inconsistency do you see in these 
formulas other than any based on atomic weights? 

6. Write the formula for thallious chloride and thallic oxide. 

7. Spinel is a mineral of varying color and the hardness of topaz. 
It may be regarded as magnesium aluminate [Mg(A10 2 ) 2 ]. Write 
the formula for an hypothetical acid of which spinel may be regarded 
as a magnesium salt. 

8. Write the formula for ammonium alum. 

v 

9. Write a graphic symbol for Ca^N" 2 4 . 

10. Correct the following equations : 

Zn + HC1 2 = 2ZnCl + H 2 . 
2K(NO) 3 + H 2 (SO) 4 = K 2 S0 4 + 2HN0 3 . 



CHAPTER XIV. 
THE FOURTH GROUP — TETRADS. 

I. CARBON. 
Symbol, C ; atomic weight, 12 ; valence, 4. 

220. Occurrence. — Two allotropic modifications of car- 
bon, the diamond and graphite, are found free in nature. 
Combined with hydrogen, carbon occurs in coal, petroleum, 
bitumen, etc. Combined with oxygen, it forms a con- 
stituent of the atmosphere upon which all vegetable life is 
directly dependent. United with oxygen and calcium, it 
is found as limestone, chalk, and marble. All animal and 
vegetable bodies contain carbon ; in fact, carbon is the 
chemical center of organic nature. When any of these 
"organic" bodies is sufficiently heated out of contact 
with oxygen there remains amorphous carbon or charcoal, 
a third allotropic variety. 

(a) The chemical identity of these several allotropic forms is shown 
by the fact that, when highly heated with oxygen, they all form the 
same compound, CO.,, 12 parts of any variety of carbon uniting with 
32 parts of oxygen to form 44 parts of the oxide. 

221. The Diamond. — Diamond is a crystalline solid, 
brilliant, transparent, and generally colorless. Diamonds 
are most frequently found in the form of rounded pebbles 
which are cut into desirable forms by pressing the surface 
of the stone against a revolving metal wheel covered with 

100 



CARBON. 197 

a mixture of diamond-dust and oil. It is the hardest 
known substance. It is a very poor conductor of heat 
and electricity and, when polished, has a magnificent 
luster and high refractive power upon light. These prop- 
erties, together with its permanence and rarity, make it 
the most precious of gems. Its density is 3.5. 

(a) The diamond undergoes no change at the ordinary tempera- 
ture, but, when heated between the carbon electrodes of a strong 
electric current, it softens, swells up, and is changed to a black mass 
resembling coke. When heated in oxygen to 800°, it burns to carbon 
dioxide. " The Regent " diamond is valued at more than half a million 
dollars. Small artificial diamonds have been produced. 

222. Graphite. — Graphite or plumbago is familiarly 
known as the black lead of the common "lead pencil." 
It is found abundantly in nature in the crystalline and 
amorphous forms, the crystals being wholly unlike those 
of the diamond. It is opaque, nearly black, and has a semi- 
metallic luster. It is very friable and has an unctuous 
feel. It is unalterable in the air at ordinary tempera- 
tures. Its density varies from 2 to 2.5. It is used in 
making pencils, lubricating machinery, in making cru- 
cibles especially for the manufacture of steel, as a stove- 
polish, and in electrotyping. Artificial graphite has been 
prepared by heating charcoal or some other amorphous 
variety of carbon in an arc furnace, or by dissolving it in 
molten iron from which the graphite separates on cooling. 

(a) For many years, graphite was supposed to contain lead; 
whence the names plumbago and black lead. 

223. Mineral Coal. — Mineral coal consists of the luxu- 
riant vegetation of past geological ages. In the interven- 



198 THE FOURTH GROUP — TETRADS. 

ing period, inconceivably long, the woody fiber, a compound 
of carbon, hydrogen, and oxygen, was, by pressure and in 
some cases by heat, changed to the various kinds of coal. 
The principal chemical change was in the gradual loss of 
hydrogen and oxygen ; the degree in which this loss took 
place determines the character of the coal produced. At 
the earlier stage of the process, the product was lignite or 
brown coal, usually found in the later geological strata. 
A further loss of hydrogen and oxygen resulted in the 
various kinds of bituminous coal. When the carbonaceous 
material was also subjected to heat, the loss of hydrogen 
and oxygen was greatest, and the resultant product was 
either anthracite or graphite. Thus there is a gradation 
of coals from anthracite down to lignite or to peat in 
which the woody fibre is but little changed. 

(a) Mingled with the carbonaceous material of the coal, there is 
always more or less earthy material, limestone, and pyrite. When 
coal is burned, these remain as ashes. In the combustion, the sulphur 
of the pyrite is converted into sulphuric acid, which, with the soot, 
chiefly caused by careless firing, often does great injury to trees, 
fabrics, etc., in large cities and manufacturing districts. 

224. Wood Charcoal. — This familiar substance is gener- 
ally prepared by the distillation or incomplete combustion 
of wood. In the distillation, the wood is decomposed in 
such a way that a part of the carbon and nearly all the 
hydrogen and oxygen are evolved as water, acetic acid, 
methyl alcohol, methane, and smaller quantities of many 
other compounds containing carbon, hydrogen, and oxy- 
gen. The greater part of the carbon remains as charcoal. 

(a) A common method of burning charcoal is to pile up sticks of 
wood in a large heap around a central flue, covering it with turf and 



CARBON. 



199 




Fig. 55. 



earth, leaving holes at the bottom for the admission of air and a hole 
at the top of the central flue. The fire is kindled at the bottom of 
the central flue, and 

the rate of combustion I 

controlled by regulat- 
ing the supply of air. 
The process often re- 
quires several weeks. 
At the proper time, all 
of the openings are 
closed and the fire 
thus suffocated. The 
method depends upon 
the fact that the vola- 
tile constituents of the 
wood are more easily combustible than is the carbon and therefore 
unite with the limited supply of oxygen. 

(&) When it is desired to save the volatile products of the distilla- 
tion, two kinds of retorts are used. One kind is made of fire-brick. 
In this case, the heat necessary for the distillation is furnished by the 
combustion of a part of the wood in the kiln or retort. By this process 
much of the alcohol is lost, and alcohol is the most valuable of the 
by-products of the distillation. Such loss is prevented by the use of 
closed retorts made of metal and heated by external firing. As no air 
is admitted to the wood that is to be charred, this process yields the 
highest proportion of the valuable volatile by-products, but the plant 
and its operation are more costly than they are in the other case. 

(c) The charcoal retains the form of the wood from which it was 
made, the shape of the knots and even the concentric rings being 
plainly visible. Its volume is about 65 or 70 per cent and its weight 
about 25 per cent of the wood from which it was formed. 



225. Bone-black. — Bone-black, which is the most im- 
portant variety of " animal charcoal," is prepared by 
charring powdered bones in iron retorts. The calcium 
phosphate of the bone remains and forms about ninety per 
cent of the black porous mass. The charcoal is conse- 
quently left in a very finely divided condition, spread 



200 THE FOURTH GROUP — TETRADS. 

over the particles of the phosphate or distributed among 
them. For this reason, it has greater absorptive and 
decolorizing power than vegetable charcoal. 

Chemical Reduction. 

Experiment 170. — Mix 2.5 grams of black copper oxide (CuO) 
with 0.25 grams of powdered charcoal. With some of the mixture, 
partly fill a small ignition-tube and heat it strongly. Metallic copper 
will remain in the tube while the carbon will unite with the oxygen 
of the CuO and escapes as a gas. The carbon has reduced the copper 
oxide, and the copper oxide has oxidized the carbon. 

226. Charcoal as a Reducing Agent. — Owing to the 
energetic union of carbon and oxygen at high tempera- 
tures, charcoal is largely used as a reducing agent. An- 
thracite and coke are also used for the same purpose. 
The preparation of metals from their ores (metallurgy) 
depends in a very large degree upon this property of 

carbon. 

Charcoal as an Absorbent. 

Experiment 171. — Break a piece of charcoal into two. Attach a 
sinker to one of the fragments and immerse it in water. Notice the 
bubbles rise as the water enters the pores of the charcoal and forces 
out the air previously absorbed. The experiment may be improved 
by placing the beaker containing the water and the carbon under the 
receiver of an air-pump and exhausting the air. 

Experiment 172. — Place the other fragment of the charcoal on the 

fire, and when it has been heated to full redness for some time, plunge 

it quickly into water. Notice that it needs no sinker to keep it 

€=^ submerged and that very few bubbles escape 

from it through the liquid. 

■tee^^^^^jjj Experiment 173. — Fill a long glass tube 

iiaMn "Cl'JVl with dry ammonia at the mercury bath. Heat 

zsffl i i l *~~ F ~'' = ^j , !L a piece of charcoal to redness to remove the 

" ~ ^=1= a h f lom its pores, and plunge it into mercury. 

Fig. 50. When the charcoal is cool, thrust it into the 



CARBON. 201 

mouth of the cylinder. The gas will be absorbed by the charcoal and 
mercury will rise in the tube. Explain. 

Experiment 174. — Repeat the last experiment, using dry hydro- 
chloric acid instead of ammonia. 

227. Charcoal as an Absorbent. — The porous nature of 
charcoal gives it a remarkable power of absorbing gases. 
Beech- wood charcoal has been known to absorb 170 times 
its own volume of dry ammonia. Other gases are absorbed 
in large but variable proportions. This power depends 
upon the fact that all gases condense in greater or less * 
degree upon the surface of solid bodies with which they 
come into contact. The more easily the gas is liquefied 
the more largely is it absorbed by charcoal. 

Charcoal as a Purifier. 

Experiment 175. — Into a bottle of hydrogen sulphide (see Experi- 
ment 260) put some powdered charcoal. Shake the bottle for a 
moment. The offensive odor of the hydrogen sulphide will disappear. 

Experiment 176. — Into the neck of a funnel, thrust a bit of cotton- 
wool and cover it to the depth of 2 or 3 cm. with powdered charcoal. 
Through this solution, pass a quantity of water charged with hydro- 
gen sulphide. The filtered liquid will be free from offensive odor. 

Experiment 177. — Place a small crucible filled with freshly ignited 
and nearly cold powdered charcoal into a jar kept supplied with 
hydrogen sulphide. When the charcoal is saturated with the gas, 
quickly transfer it to a jar of oxygen. The charcoal will burst into 
vivid combustion. 

228. Charcoal as a Purifier. — By condensing offensive 
and injurious gases and bringing them into intimate con- 
tact with condensed oxygen, charcoal acts as an energetic 
purifier. The fetid products of animal and vegetable 



202 



THE FOURTH GROUP — TETRADS. 



decay are not only gathered in but actually burned up. 
This property is retained by the charcoal for a long time 
and, when lost, may be restored by ignition. This oxidiz- 
ing power of charcoal forms the foundation of much of 
the utility of charcoal filters for water. 



Charcoal Filters. 

Experiment 178. — Place a dilute solution 
of the blue compound of iodine and starch 
(see Experiment 102), of indigo dissolved 
in Nordhausen acid, of cochineal, and of 
potassium permanganate in each of four 
flasks. To each, add recently ignited bone- 
black. Cork the flasks, shake their contents 
vigorously, and pour each liquid upon a 
separate filter. The several filtrates will be 
colorless. If the first part of any filtrate is 
colored, pour it back upon the filter for 
refiltration. 




229. Charcoal as a Decolorizer. — As illustrated in the 
above experiment, charcoal, and especially animal charcoal, 
is able to remove the color as well as the odor from many 
solutions. This power seems to depend more upon the 
adhesion between the carbon and the particles of coloring 
matter than upon oxidation. Brown sugar is purified by 
filtering its colored solution through layers of bone-black. 
Bone-black is also largely used in decolorizing vaseline 
and other petroleum products. If ale or beer is treated 
thus, it loses both its color and its bitter taste. This 
property of charcoal is utilized in the preparation or 
purification of many chemical or pharmaceutical com- 
pounds. 



CARBON. 



203 



Lampblack. 

Experiment 179. — Set fire to a lump of rosin and hold a cold plate 
over the flame. Soot will be deposited upon 
the plate. 

Experiment 180. — Press a spoon or a plate 
down upon a candle-flame so as nearly to 
extinguish the flame. Soot will be deposited 
upon the spoon or the plate. 

Experiment 181. — Partly fill a lamp with 
spirit of turpentine, light the wick, and cover 
the lamp with a bell-glass or a wide-mouthed ■ 
jar. Thrust a pencil or a crayon under one 
edge of the bell-glass so as to raise it from 
the table and to admit a small supply of air 
to the flame. Soot will collect upon the sides 
of the bell-glass. 




Fig. 58. 



230. Lampblack. — When a hydrocarbon, like rosin, 
turpentine, wax, petroleum, etc., is burned, the hydrogen 
is first oxidized. If the supply of oxygen is insufficient 
for the complete combustion, the carbon set free by the 
decomposition of the compound will be left in a finely 
divided amorphous state, as soot or lampblack. The same 
effect will appear if the temperature of the name is reduced 
below that at which carbon burns, as was the case in 
Experiment 179. Lampblack is manufactured on the 
large scale by burning tar, rosin, turpentine, petroleum, 
or natural gas in a supply of air insufficient for complete 
combustion, and leading the smoky products into large 
chambers where they are deposited. It is largely used as 
a pigment, and in the manufacture of india and printer's 
inks, and of electric-light carbons. 

Note. — Coke aud gas-carbon are two other varieties of amorphous 
carbon. See § 268 (ft). 



20i THE FOURTH GROUP — TETRADS. 

231. Other Properties of Carbon. — Carbon, in all of its 
forms, is practically infusible and non-volatile at ordinary 
high temperatures, but it is volatile at the high tempera- 
ture of the electric furnace. It is insoluble in ordinary 
solvents, but dissolves in many metals melted at high 
temperatures. Although it has great chemical activity at 
high temperatures, it seems to be uualterable at the ordi- 
nary temperature of the air. The lower ends of stakes 
and fence posts are often charred before embedding them 
in the earth to render them more durable. Charred piles 
driven in the river Thames by the ancient Britons in 
their resistance to the invasion of their country by Julius 
CaBsar, about 5± B.C., are still well preserved. Perfectly 
legible manuscripts, written in ink made of lampblack, 
have been exhumed with Egyptian mummies. 

Note. — Binary compounds of carbon were formerly called car- 
burets. 

EXERCISES. 

1. Is charcoal lighter or heavier than air? How may it be dis- 
solved? 

2. What becomes of a piece of wood burned in the open air? 

3. State the useful properties of charcoal. 

4. State the characteristics of three allotropic modifications of 
carbon. 

5. How would you prepare a solution of hydrochloric acid? 

6. Give a proof of the fact that diamond is carbon. 

7. In what way does the disinfecting power of charcoal differ from 
that of chlorine ? 

8. Is carbon a bleaching agent? Why? 

9. Symbolize compounds of C iv with L', M", Q"', R iv , and X v , 
these last letters symbolizing hypothetical elements. 

10. Can a hydrogen-flame deposit soot? Why? 

11. Write the systematic chemical name and the molecular formula 
for alum. 



CARBON OXIDES, ETC. 205 

II. CARBON OXIDES, ETC. 

232. Carbon Oxides. — There are two oxides of carbon, 
having the molecular symbols CO and C0 2 . The first 
may be considered the product of incomplete combustion 
of carbon ; the second, that of complete combustion. Both 
of them are gaseous. 

Preparation of Carbon Monoxide. 

Experiment 182. — Pulverize 5 grams of potassium ferrocyanide 
and place it in a Florence flask of about 250 cu. cm. capacity. Add 
25 en. cm. of strong sulphuric acid and heat gently, removing the 
lamp as soon as the gas begins to come off rapidly. The gas may be 
passed through a solution of potassium hydroxide (KOII) and col- 
lected over water. 

Experiment 183. — Place a small quantity of oxalic acid (H 2 C 2 4 ) 
in a small Florence flask, add enough strong sulphuric acid to cover 
it, place upon a sand-bath, and heat gently. The sulphuric acid 
removes the elements of water from the H 2 C 2 4 , and leaves a mixture 
of CO and C0 2 . 

H 2 C 2 4 4- beat = C0 2 + CO + H 2 0. 

The dioxide may be removed by passing the mixed gases through a 
solution of KOH, as in the last experiment, or by collecting over water 
rendered alkaline by such a solution. 

233. Carbon Monoxide. — Carbon monoxide (carbon 
protoxide, carbonic oxide, carbonous oxide, carbonyl, CO) 
yields, when burned, the characteristic blue flame often 
seen playing over a freshly-fed coke or anthracite fire. 
It may be prepared by passing steam over highly heated 
carbon, as will be explained in the description of the manu- 
facture of water-gas. 

234. Properties. — Carbon monoxide is a colorless, odor- 
less, poisonous gas. It is a little lighter than air, having a 



206 THE FOURTH GROUP — TETRADS. 

density of 14. It is scarcely soluble in water, but is 
wholly absorbed by an acid or an ammoniacal solution 
of cuprous chloride (CuCl). It is liquefiable only with 
extreme difficulty. Like hydrogen, it does not support 
combustion, but is combustible. It burns with a pale-blue 
flame and yields carbon dioxide (C0 2 ) as the sole product 
of its combustion. It is an active poison and doubly dan- 
gerous on account of its lack of odor. One per cent of it 
in the air is fatal to life, which it destroys, not merely 
by excluding oxygen (suffocation), as hydrogen, nitrogen, 
etc., do, but by direct action as a true poison. It acts as 
a poison by uniting chemically with the red corpuscles of 
the blood, thus destroying their oxygen-carrying capacity. 
For this reason, the best antidote is the free inhalation 
of pure oxygen. As this gas is formed in charcoal and 
anthracite fires, and as it passes easily through faulty joints 
and even through cast iron plates heated to redness, it is 
the frequent cause of oppression, headache, and danger in 
stove- or furnace-heated and ill- ventilated rooms. Carbon 
monoxide is rightly chargeable with many of the ill effects 
usually attributed to the less dangerous dioxide. 

(a) Carbon monoxide is readily oxidized to the dioxide, and the 
dioxide is easily reduced to the monoxide. Thus, when air enters at 
the bottom of an anthracite fire, the oxj^gen unites with the carbon to 
form carbon dioxide. As this gas rises through the glowing coals 
above, it is reduced. 

C0 2 + C = 2CO. 

When this heated monoxide comes into contact with the air above 
the coals, it burns with its characteristic blue flame. 

CO + o = co 2 . 

If the oxygen necessary for this second combustion is not present, 
the dangerous monoxide will escape. 



CARBON OXIDES, ETC. 



207 



(b) Under the influence of sunlight, two volumes of carbon monox- 
ide unite directly with two volumes of chlorine, forming tw r o volumes 
of carbonyl chloride or phosgene gas (COCl 2 ). It will be noticed 
that here, CO acts as a dyad compound radical. 

Chemical Reduction. 

Experiment 184. — Pass a stream of carbon monoxide over some 
copper oxide (CuO) heated in a hard-glass bulb-tube, and thence into 
clear lime-water. Write the reaction. 

235. Uses. — Carbon monoxide is an important agent in 
many metallurgical operations, on account of its power of 
reducing metallic oxides. It furnishes the principal fuel 
value of " producer-gas," and is one of the important con- 
stituents of coal-gas and of water-gas. 



Preparation of Carbon Dioxide. 

Experiment 185. — Repeat Experiment 40. The white precipitate 
that causes the turbidity is calcium carbonate. 

Ca(OH) 2 + CO, = CaC0 3 + H 2 0. 




Fig. 59. 

Experiment 186. — Mix 11 grams of red oxide of mercury and 0.3 
grams of powdered charcoal. Heat the mixture and collect over water 
the gas that is given off. Test the gas with lime-water. The oxygen 
that united with the carbon came from the mercury oxide. 

2HgO + C = C0 2 + 2Hg. 



208 



THE FOURTH GROUP — TETRADS. 



Examine the ignition-tube carefully for traces of metallic mercury. 
In similar manner, many solid, liquid, and gaseous bodies that are 
rich in oxygen give it up readily to unite with carbon and form carbon 
dioxide. In other words, such bodies are " reduced " by the carbon. 

Experiment 187. — Into a bottle, arranged as described in § 21, put 
a handful of small lumps of marble (CaCOo). Cover the lumps with 
water, and add small quantities of hydrochloric acid from time to 
time as may be needed to secure a continued evolution of gas. Col- 
lect several bottles of the gas over water. As carbon dioxide is heavier 
than air, it may be collected by downward displacement, as we col- 
lected chlorine. 

CaC0 3 + 2HC1 = CaCl 2 + H 2 + CO,. 

Note. — Hydrochloric acid is better than sulphuric acid in prepar- 
ing C0 2 from CaC0 3 because CaCl 2 is more easily soluble than is 
CaS0 4 . Old mortar, powdered oyster-shells, coral, or limestone will 
answer instead of marble, but marble 
is preferable as there is less frothing. 
Experiment 188. — Arrange, as 
shown in Fig. 60, two flasks contain- 
ing lime-water. Apply the lips to the 
tube and inhale and exhale air 
through the apparatus. In a few mo- 
ments, the lime-water in C, through 
which the air passes from the lungs, 
will become milky, while that in B, 
through which the air passes to the 
lungs, remains clear. 

Experiment 189. — Dissolve 50 cu. 
cm. of molasses in about 400 cu. cm. 
of water and place the liquid in a 




Fig. GO. 



half-liter flask. Add a few spoonfuls of 
yeast, cork the flask, and connect its 
delivery-tube with a small bottle, b, filled 
with water. A delivery-tube should 
extend from the bottom of b into a cup, c. 
Keep the apparatus at a temperature of 
21° or 22°, and fermentation will soon 
begin. As the liquid in F ferments, 
bubbles of gas will rise through it and 




CARBON OXIDES, ETC. 209 

pass over into b, forcing a corresponding quantity of water into c. 
When b is nearly full of this gas, remove its stopper and test its 
contents with a name and with lime-water. The gas is C0 2 . Let 
the liquid in F remain in a warm place for two or three days. Cork 
the bottle and save the liquid for future use. The sugar (C 6 H ]2 (J ) 
of the molasses was decomposed into alcohol, (C 2 H 6 0) and C0 2 . The 
alcohol remains dissolved in the liquid in F. 

236. Carbon Dioxide. — Carbon dioxide (carbonic anhy- 
dride, C0 2 , often improperly called carbonic acid or car- 
bonic acid gas) is formed when carbon or any carbon 
compound is burned under conditions that afford an 
~, abundant supply of oxygen. It is produced in large 
quantities in burning limestone to quicklime. 

CaC0 3 + heat = CaO + C0 2 . 

It may be easily obtained by the decomposition of carbon- 
ates, such as marble, chalk, or limestone. It is a product 
of animal respiration, of fermentation, and of the decay 
and putrefaction of all animal and vegetable matter. It 
is a constituent of the atmosphere, and of carbonates that 
are found in extensive layers of the earth's crust, and is 
found in most natural waters. It issues from the earth in 
some volcanic regions, and is a principal constituent of all 
furnace gases. It is frequently met with in mines, the 
dreaded choke-damp. 

Physical Properties of Carbon Dioxide. 

Experiment 190. — Suspend a light glass or paper jar from one end 
of a scale-beam and counterpoise it in any convenient way. Pour 
C0 2 into the jar and it will descend (see Fig. G2). 

Experiment 191. — Partly fill a wide-mouthed jar with C0 2 . Throw 
an ordinary soap-bubble into the jar. It will float on the surface of 
the heavy gas. 

SCHOOL CHEMISTRY — 14 



210. 



THE FOURTH GROUP — TETRADS. 



Experiment 192. — Fill a long-necked Florence flask with C0 2 . 
Pour in a little water, close the mouth with cork or finger, shake the 
bottle, and then open the mouth under water. Part of the gas will 
have been dissolved in the water, and more water will enter the flask 
to fill the partial vacuum. Close the flask, shake it again, and once 
more open its mouth under water. More water will enter. In this 




way, all of the gas may be dissolved in water. After agitating C0 2 
and water in a test-tube closed by the thumb or palm of the hand, the 
tube and contents may be held hanging from the hand, supported by 
atmospheric pressure. 



237. Physical Properties. — Carbon dioxide is a color- 
less gas, so heavy that it may easily be poured from one 
vessel to another. Its density is 22, it being one and 
a half times as heavy as air. It, therefore, diffuses but 
slowly, and often accumulates in wells, mines, and caverns 
(see article, " Grotto del Cane," in any cyclopaedia). Under 



CAEBON OXIDES, ETC. 211 

a pressure of fifty atmospheres at the ordinary tempera- 
ture, it condenses to a liquid. This liquid has a density 
of 0.83, and its boiling-point is — 78°. Its rapid expan- 
sion, when released from pressure, produces a temperature 
low enough to freeze part of itself to a white, snowlike 
mass that melts at — Qo°. This solid carbon dioxide, 
when mixed with ether, produces a degree of cold that 
quickly freezes mercury, and in a vacuum, yields a tem- 
perature of — 110°. Liquid carbon dioxide contained in 
strong steel cylinders is a common article of commerce. 
The gas is soluble in water, volume for volume, at ordinary 
temperatures and pressures ; more largely at lower tem- 
peratures or higher pressures. It imparts a sparkling 
appearance and pleasant taste to water and contributes 
to the refreshing qualities of aerated beverages of all 
kinds. 

Chemical Properties of Carbon Dioxide. 

Experiment 193. — From a large vessel filled with C0 2 , dip a tum- 
blerful of the gas and pour it upon the flame 
of a taper burning at the bottom of another 
tumbler. The flame will be extinguished . 

Experiment 194. — Fasten a tuft of cotton- 
wool to the end of a w T ire or a glass rod, dip 
it into alcohol, ignite it, and quickly thrust 
the large flame into a bottle of C0 2 . The 
flame will be instantly extinguished. 

Experiment 195. — Fasten a piece of mag- 
nesium ribbon, 15 or 20 cm. (6 or 8 in.) long- 
to a wire, ignite the ribbon, and quickly plunge it into a jar of C0 2 . 
It will continue to burn, leaving white flakes of magnesium oxide 
(MgO) mixed with small particles of black carbon. Rinse the jar 
with a little distilled water, pour the water into an evaporating-dish, 
add a few drops of hydrochloric acid and heat. The MgO will dis- 
solve, leaving the black particles floating in the clear liquid. 




Fig. 63. 



212 THE FOURTH GROUP — TETRADS. 

Experiment 196. — Pass a stream of C0 2 through lime-water. Notice 
that the formation of calcium carbonate (CaC0 3 ) soon renders the 
water turbid, but that, the current being continued, the turbidity soon 
disappears. When the water has thus lost its milky appearance, boil 
it. The excess of C0 2 will escape in bubbles; the liquid will become 
turbid again and deposit a precipitate of CaC0 3 . This illustrates the 
way in which lime may be carried in solution in spring waters and 
deposited as travertine when these waters are exposed to the air or 
heated in boilers. 

238. Chemical Properties. — Carbon dioxide, being the 
product of complete combustion, is incombustible. It is 
a non-supporter of ordinary combustion. Its solution in 
water may be considered as containing true carbonic acid 
(H 2 C0 3 ). The salts of this unstable acid are called car- 
bonates. The gas may be completely absorbed by a solu- 
tion of potassium hydroxide with which it unites to form 
potassium carbonate. 

2KOH 4- C0 2 = K 2 C0 3 + H 2 0. 

2KOH + H 2 C0 3 = K 2 CO s + 2H 2 0. 

Note. — As carbonic acid is dibasic, there are two types of car- 
bonates (§§ 92, 94). Thus we have normal sodium carbonate 
(Na 2 CO s ), and acid sodium carbonate (sodium bicarbonate, NaHC0 3 ). 

239. Uses, etc. — Carbon dioxide has been successfully' 
used for extinguishing fires in coal mines. The efficiency of 
many of the common, portable " fire extinguishers" depends 
partly upon this same property of carbon dioxide. Water 
charged with large quantities of the gas is sold under the 
meaningless name of "soda water." While the dioxide is 
not poisonous when taken into the stomach, it is injurious 
when breathed into the lungs, although the bad effects of 
living in ill- ventilated rooms are due less to carbon dioxide 



CARBON OXIDES, ETC. 213 

than to other waste products and living organisms given 
off in breathing. When largely diluted with air, carbon 
dioxide has a narcotic effect and its presence to the extent 
of nine or ten per cent of the atmosphere is sufficient to 
cause suffocation and death. While thus destructive of 
animal life it is essential to vegetable existence. 

Water containing carbon dioxide in solution is capable 
of dissolving calcium carbonate and other substances that 
are insoluble in pure water. In this way, many rocks are 
disintegrated, stalagmites and stalactites formed, or the 
soil fitted for the needs of plants. The gas is also used in 
"corroding"' lead for use as a paint ("white lead*'), and 
in the preparation of sodium and other carbonates. 

240. Tests. — The precipitation of calcium carbonate 
when carbon dioxide is passed through lime-water or 
shaken with it, is the most common test for the gas. The 
presence of carbonates is indicated by the escape of carbon 
dioxide with effervescence when they are treated with 
hydrochloric, nitric, sulphuric, or any other strong acid. 

241. Cyanogen. — This compound of carbon and nitro- 
gen (CN) is an univalent radical (— C = N). It was the 
first compound radical isolated, and has played a prominent 
part in the development of synthetical "organic" chemis- 
try. Under ordinary circumstances, carbon and nitrogen 
do not unite, but at very high temperatures and in the 
presence of certain metals they form compounds known 
as cyanides of those metals. Cyanogen is generally pre- 
pared by heating the cyanide of gold, silver, or mercury, 
and collecting over mercury. 

Hg(CN) 2 =Hg+(CN) 3 . 



214 THE FOURTH GROUP — TETRADS. 

It is a colorless, poisonous, inflammable gas, easily soluble 
in water or in alcohol. It acts like a monad element, 
forming compounds corresponding to the chlorides, e.g.: 

Free chlorine Cl 2 

Potassium chloride . . . KC1 
Hydrochloric acid .... HC1 



Free cyanogen .... (CX) 2 
Potassium cyanide . . . KCN 
Hydrocyanic acid . . . HCX 



242. Hydrocyanic Acid. — Hydrocyanic acid is a vola- 
tile, inflammable, intensely poisonous liquid ; " the onset of 
symptoms is reckoned by seconds rather than by minutes." 
Its aqueous solution is well known as prussic acid; it is 
used "in medicine. It occurs in nature in bitter almonds 
and in the leaves of the cherry, laurel, etc. It may be 
prepared by passing a current of hydrogen sulphide over 
heated mercury cyanide, or by treating a cyanide witli 
sulphuric or with hydrochloric acid. (Dangerous ; do 
not try it.) 

Hg (CX) 2 + H 2 S = 2HCN + HgS. 
2KCN 4- H 2 S0 4 = 2HCN + K 2 S0 4 . 
KCN + HC1 = HON + KC1. 

243. Other Cyanides. — Potassium cyanide has already 
been considered (§ 164). Potassium ferroe}~anide and 
potassium ferricyanide will be considered further in a later 
chapter. At present, it will be enough to say that this 

. ferrocyanide is industrially produced from potassium car- 
bonate, iron-filings, and animal refuse, and that it is the 
common starting-point for the production of the other 
cyanides by laboratory methods. 

244. Tests. — With solutions of silver nitrate, the cya- 
nides produce precipitates insoluble in nitric acid. The 
odor of the acid is also characteristic. 



CARBON OXIDES, ETC. 215 

EXERCISES. 

1. Explain and illustrate what you understand by valence. 

2. Write graphic formulas and the names of H C0 3 , A T a.,COo, and 
NaHC0 3 . 

3. Write an equation showing what becomes of the C0 2 removed 
from the CO in Experiment 183. 

4. Give the densities of C0 2 , NH 3 , HC1, and H 2 , with the principle 
by which they are easily determined. 

5. When free cyanogen is mixed with an excess of oxygen and an 
electric spark passed through the mixture, an explosion occurs. On 
cooling, the residual gases, one of which is nitrogen, have the same 
volume as the original mixed gases. Write the reaction. 

6. What is the weight of a liter of cyanogen gas ? 

7. How would you prove the solubility of HC1, NH 3 , and C0 2 ? 

8. (a) What weight of carbon dioxide would be produced by 
burning 5 grams of carbon? (b) What volume? 

9. (a) What weight of C0 2 may be obtained from 100 grams of 
CaC0 3 by the action of HC1 ? (b) What volume ? 

10. What is the weight of 10 liters of C0 2 ? 

11. (a) If 20 cu. cm. of CO and 10 cu. cm. of oxygen are mixed in 
an eudiometer and an electric spark is passed, what will be the name 
and volume of the product? (b) Write the reaction, (c) If this 
product is agitated with a solution of potassium hydroxide, what will 
be the effect upon the gaseous volume ? 

12. How is nitric acid prepared? Write the reaction. 

13. Give the laboratory mode of liberating carbon dioxide with the 
reaction, and the percentage composition of the source of the gas. 

14. How many liters of C0 2 can be obtained from 200 grams of 
CaC0 3 ? 

15. Describe a method of preparing oxygen, and express, by sym- 
bols, the changes that take, place. 

16. Modify Experiment 170 by providing the ignition-tube with a 
bent delivery-tube, and determine the nature of the gas evolved. 
Write the reaction for the chemical changes involved in the reduction. 

17. How much oxygen is needed to burn 500 grams of charcoal? 
How many liters of C0 2 will be produced ? 

18. What volume of air will be required for the combustion of 100 
tons of coal, assuming that the coal is pure carbon and burns to 
carbon dioxide? 



216 THE FOURTH GROUP — TETRADS. 

19. Calculate the weight of air required to burn a ton of coal 
having the percentage composition: C, 88.42; H, 5.61; (), etc.. 5.97. 

20. Write the reaction for the combustion of spirit of turpentine 
in Experiment 181. Assume that the turpentine has the composition 

indicated by the formula C 10 H 1(; . 

III. THE RELATION OF CARBON TO VEGETABLE AND 
ANIMAL LIFE. 

245. Constituents of Organized Matter. — Every com- 
pound formed by the action of a living organism, i.e., 
every animal and vegetable substance, contains carbon as 
an essential constituent. In addition to the carbon, many 
of them contain only hydrogen, oxygen, and nitrogen ; 
some of them only hydrogen and oxygen. A few contain 
also phosphorus or sulphur, or both. Most of them also 
contain small proportions of mineral substances that form 
the ash when the organic matter is burned or otherwise 
fully oxidized. The bones of animals consist largely of 
such mineral constituents, containing large proportions 
of the phosphates and carbonates of calcium and other 
metals. 

246. Variety of Carbon Compounds. — The number of 
the carbon compounds formed in living animal and vege- 
table bodies is greater than the number of the compounds 
of all the other elements taken together. Until recently, 
none of the substances formed by living organisms could 
be produced by any other means. This fact was consid- 
ered so important that the carbon compounds were placed 
in a class by themselves and studied under the style and 
title of " organic chemistry." It was assumed that they 
were essentially the products of a so-called "vital force." 



PLANT AND ANIMAL FOOD. 217 

Since it has become possible artificially to produce many 
of them, the old distinction between the organic and. the 
inorganic branches of chemistry has been abandoned. 
When the term " organic chemistry " is now used, it is 
with a changed meaning — the chemistry of the com- 
pounds of carbon. 

(a) The laboratory production of a typical compound of this class, 
i.e., the synthetic preparation of an " organic " compound from " dead 
matter," was first accomplished in 1828 by Friedrich Wohler, a Ger- 
man chemist. 

247. The Food of Plants. — About three parts in ten 
thousand parts of the atmosphere, by volume, is carbon 
dioxide. This may seem an insignificant proportion until 
we realize that each cubic mile of the atmosphere near the 
earth contains more than seven hundred tons of carbon. 
All the carbon essential to plant life comes from this 
atmospheric supply. Plants breathe in the air through 
the pores of their leaves. Under the influence of sunlight, 
the carbon dioxide thus inhaled is broken up, the carbon 
being appropriated as a constituent of living tissue, while 
the freed oxygen is returned to the air. As only about 
twenty per cent of green wood is carbon, the supply of 
carbon in the atmosphere within a mile of the surface 
of the earth is adequate for a considerable growth of 
forest. After life ceases, all of this carbon is returned 
to the atmosphere as carbon dioxide — the ultimate prod- 
uct of all combustion and decay of carbon compounds. 

(a) It is probable that in former ages the atmosphere contained a 
larger proportion of carbon dioxide than it does at present, that vege- 
tation was more luxuriant then than now, and that carbon was stored 
away as coal, petroleum, and gas. 



218 THE FOURTH GROUP TETRADS. 

248. The Food of Animals. — The food of animals comes, 
directly or indirectly, from plants. In the animal body 
much of the food taken is burned, the oxidation furnishing 
the heat necessary for animal warmth. The carbon diox- 
ide produced by this combustion is returned through the 
lungs to the air. 

249. Solar Energy. — Carbon is the great agent for 
transferring the energy of the sun to the living animal. 
The energy of sunlight expended in breaking up the 
carbon oxide that is absorbed by the leaf is stored up as 
potential energy in the vegetable tissue, and again set free 
as heat in the animal body. The sun's energy that is 
transformed into the chemical energy of carbon compounds 
that become parts of vegetable tissue is the physical source 
and foundation of all life. The plant breathes in carbon 
dioxide ; the animal breathes out carbon dioxide. Each 
carbon particle involved may go through the same cycle 
of changes again aud again, carrying with it on each 
round the energy necessary for the maintenance of vege- 
table and animal life. 

EXERCISES. 

1. Assuming that a square meter of leaf will decompose a liter 
of carbon dioxide per hour, what weight of carbon will be assimilated 
in an hour by 1,000 trees, each of which has 100,000 leaves, each leaf 
measuring 25 sq. cm.? 

2. Is Hg(CX) 2 a mercurous or a mercuric compound? What is 
its name? 

3. Describe the usual method of preparing chlorine, and write the 
reaction. Find the percentage of chlorine in the substance that fur- 
nishes it. 

4. Zinc nitrate and potassium carbonate react as follows : 

Zn(NO,) 2 + K 2 C0 3 = ZnCO ;3 + 2 KN0 3 . 
How much Zn(NO a ) 2 is required to give 103.17 grams of ZnC0 3 ? 



HYDROCARBONS IN HOMOLOGOUS SERIES. 219 

5. How much ZnC0 3 may be obtained from 156 grams of 
Zn(X0 3 ) 2 ? 

6. How much K.,C0 3 is needed to decompose 75 grams of 
Zn(NCg 2 V 

7. What quantity of potassium nitrate will result ? 

8. How much K 2 CO g must be used to obtain 51 grams of ZnC0 3 ? 

9. How much potassium nitrate will be produced? 

10. Why is the term "organic chemistry" less frequently used 
than formerly ? 

11. Trace the muscular energy of a carnivorous animal to solar 
energy as its source. 

12. When oxygen is prepared by heating manganese dioxide, Mn 3 4 
is formed. Write the reaction. 

13. Complete the following equation with the formula for a single 
molecule : 

Ba0 2 + 2HC1 = BaCl 2 + 

IV. HYDROCARBONS IN HOMOLOGOUS SERIES. 

250. The Hydrocarbons. — ■ The compounds of hydrogen 
and carbon are called hydrocarbons. They and their 
derivatives are so numerous that an attempt to name 
them would lead beyond the proper limits of an ele- 
mentary text-book. Fortunately, the relations between 
them are so simple that their study is not difficult. They 
exist in great quantities in nature as the sole constituents 
of petroleum and natural gas, and as the principal con- 
stituents of the various asphalts and similar substances. 
They are also formed when most carbon compounds are 
highly heated without access of air, as in the manufacture 
of coal-gas. They have been classified, each individual 
member of a series differing but little in composition and 
properties from its neighbors in that series. 

251. Hydrocarbon Skeletons. — The great diversity of 
the hydrocarbon compounds arises from the fact that 



220 THE FOURTH GROUP — TETRADS. 

carbon atoms have the peculiar property of combining 
with themselves to form a variety of molecular skeletons 
to which other elements may be attached, forming com- 
pounds so numerous that their names and brief descrip- 
tions would fill many volumes. The single atom of carbon 
is capable of fixing four atoms of hydrogen, and is, there- 
fore, quadrivalent. It forms but one compound with 
hydrogen, CH 4 . 

(a) Two atoms of carbon may be united together with a single 

I I 
bond, forming — C — C — , leaving six bonds unsaturated. If they 

i i 

i i 

are united with two bonds, C = C, four bonds are left open. When 

I I 
they are united by three bonds, — C = C — , only two bonds are left 
open. We have, therefore, the three different compounds, ethane 
(C 2 H fi ), ethelyne (C 2 H 4 ), and acetylene (C 2 I1 2 ), each molecule contain- 
ing two atoms of carbon that unite with hydrogen as above. 

(b) Three atoms of carbon give the following possible skeletons : 

III III I 

_C — C — C — ; _ C = C — C — ; — C = C — C— . 
Ill I I 

C 3 H 8 C,II G C,II 4 

CJW2 C n II „ C, t H 2 „_ 2 

(r) In a similar way, the higher members give rise to several 
series, each differing from the next by H 2 . There are, in this way, 
the following: CJI 2n+2 ; C„II n ; C„II 2n _ 2 ; C w H 2n _ 4 ; C M H 2n _ 6 ; and 
so on with no exception up to CJHfeh-as. 

252. Isomers. — The powder of carbon atoms to unite 
thus with each other almost without limit is not possessed 
by any other element. It is the cause of the vast number 
of the carbon compounds. The fact that carbon atoms 
combine with each other in different ways results also 



HYDROCARBONS IN HOMOLOGOUS SERIES. 221 

in the formation of many compounds of the same compo- 
sition, but with different physical properties. These com- 
pounds that have the same percentage composition and that 
differ in the arrangement of the atoms in the molecule, and 
hence have different physical properties, are called isomers. 

(«) Isomers that differ in molecular weight are called polymers, of 
which acetylene (C 2 H 2 ) and benzene (C 6 H 6 ) are examples. Isomers 
that have the same molecular weight are called metamers, of which 
ammonium cyanate (NH 4 CNO) and urea [(NH 2 ) 2 CO] are examples. 
In like manner, aldehyde and ethylene oxide have the same molecular 
weight, and their elements are combined in the same proportion 
(C 2 H 4 0), but they differ widely in their chemical properties. 

253. Molecular Structure. — These isomeric forms in- 
crease in number very rapidly as the complexity of the 
molecule increases. There are three known isomers hav- 
ing the formula of C 5 H 12 ; five, having the formula C 6 H 14 . 
There are nine possible forms of C 7 H 16 , four of which are 
known. It has been calculated that for the hydrocarbon 
C 13 H 28 , there are 799 possible isomers. In such ways, an 
almost endless variety of carbon compounds arises. 

(a) The recognized variations in molecular structure that underlie 
isomerism have made it important for chemists to resolve the empiri- 
cal formulas into atomic groups that shall at least suggest some of the 
known facts in any given case. By way of illustration, we may take 
one of these isomeric compounds, acetic acid (C 2 H 4 () 2 ). Experiment 
shows that acetic acid is monobasic ; i.e., that only one of its four 
hydrogen atoms can be replaced by a metal to form a salt. This 
suggests that one of the four hydrogen atoms is held in the molecule 
in a way different from the way or ways in which the other three are 
held. This fact is expressed by writing the formula for acetic acid, 
H(C 2 H 3 2 ). 

It is also possible to substitute one atom of chlorine for one of 
hydrogen, and one of oxygen in the acetic acid molecule, yielding 
C 2 H 3 0C1. jSTo greater part of the hydrogen and oxygen can be thus 



222 THE FOURTH GROUP — TETRADS. 

replaced, and the properties of the derived substance indicate that the 
hydrogen atom now displaced in company with the oxygen atom is 
the same one that in the previous experiment was replaced by the 
metal. These facts are expressed by writing the formula for acetic 
acid HO(C 2 H 3 0). 

The synthetic preparation of acetic acid shows that the group CH 3 
passes without change from one of the factors into the product, 
HO(C 9 H 3 0). This fact. leads to the separation of the group C 2 H,0 
into two groups, CH 3 and CO. 

The original molecule, C 2 H 4 2 , has now been resolved into the 
three atomic groups, HO, and CO, and CH r This final result is 
expressed by the structural or constitutional formula for acetic acid, 
CH 3 - CO - OH, or CH 3 • CO ■ OH. 

(b) In some such way as that just described, the molecular structure 
of many complex substances has been determined. Such theoretic 
conceptions have led the way to some of the most brilliant achieve- 
ments of synthetic chemistry. 

254. The Leading Hydrocarbon Series. — The most im- 
portant of these are the following : 

The marsh-gas series, having the composition C„H 2h+2 . 
The ethylene series, having the composition C n H 2n . 
The acetylene series, having the composition C n H 2 „_ 2 . 
The benzene series, having the composition C„H 2n _ 6 . 

(a) Examples of the above are included in the following list : 

C„H 2n+2 ; methane or marsh-gas (CH 4 ), ethane (C 2 H (; ), etc. 

C n H 2rt ; methene 1 or methylene (CH 2 ), ethene or ethylene (C 2 II 4 ), etc. 

C„H 2n _ 2 ; ethine or acetylene (C 2 H 2 ), allylene (C 3 H 4 ), etc. 

C n H 2rt _ 4 ; very few are known. 

C n H 2n _ 6 ; benzene (C„H 6 ), toluene (C r Il 8 ), etc. 

(b) A series of carbon compounds, each differing from the next in 
the series by CH 2 , is called an homologous series. 

255. Petroleum. — This liquid mineral which, since 
1860, has been abundant in the markets of the world and 

l CH 2 exists only \n combination. 



HYDROCARBONS IN HOMOLOGOUS SERIES. 223 

has come into use in many ways, is chiefly a mixture of the 
marsh-gas and the ethylene series of hydrocarbons. Some 
of these constituents are gaseous under ordinary conditions 
and pass off when the pressure under which they were 
confined in the earth is removed. A mixture of petroleum 
vapors with air is explosive and the thicker constituents 
of the native oil clog lamps and wicks. The petroleum 
therefore needs refining to fit it for domestic use. 

256. Refining Petroleum. — The crude petroleum is 
pumped from wells into storage tanks where water, dirt, 
and other impurities separate and settle to the bottom. 
The clear oil is then distilled from large iron retorts and 
thus separated into several products as the density of the 
distillate changes (see Fig. 64). As the first four mem- 
bers of the marsh-gas series are gaseous under ordinary 
conditions, they are not now taken into consideration 
although, in greater or less quantities, they are probably 
held in solution. Among these distillates are the following : 

(«) Naphtha Group. — This includes the lighter oils from pentane 
to nonane inclusive (see § 257). Their boiling-points range from 0° 
to about 150°. The most important of these is gasolene, which forms 
a considerable proportion of most petroleums. It is extensively used 
in the extraction of oils, for cleansing purposes, for prime motors or 
engines, and as a fuel in stoves peculiarly constructed for this purpose. 
Its great volatility, or low boiling-point, renders hazardous its use, 
especially by those who are lacking in intelligent care. 

(b) Illuminating-oils. — These are sold as kerosene, paraffin oil, etc. 
The safety of illuminating-oils is determined by the flashing-point, or 
the temperature at which they give off an inflammable vapor. In 
most states, inspectors are appointed to see that only such as bear the 
legal test, as to flashing-point, are sold for illuminating purposes. 

(c) Lubricating-oils and Vaseline. — These are the heavier oils 
occurring in petroleum. 



224 THE FOURTH GROUP TETRADS. 




' 




HYDROCARBONS IN HOMOLOGOUS SERIES. 



225 



(d) Solid Paraffins. — These amount to about 2 per cent of the 
petroleum, and are used for candle-making, coating for the ends of 
matches to cause them to kindle readily, etc. 

The proportion of these various constituents existing in 
crude petroleum is widely different in the supplies obtained 
from different localities. After the volatile constituents 
are thus removed by fractional distillation, there remains 
a solid, black residue that is nearly pure carbon. This 
coke is used in the manufacture of carbons for arc electric 
lighting, for electric batteries, and for electrolytic cells. 
Each of the fractions is freed from the colored and ill- 
smelling compounds and otherwise purified by washing 
with sulphuric acid, then with alkali, and then with water. 
The heavy, dark-colored products are sometimes made 
light-colored by filtering them through bone-black or 
through fullers' earth and bleaching in sunlight. 



257. The Paraffins. — The marsh-gas series (C w H 2ra+2 ) 
are called paraffins because of their chemical inertness 
Qparum, little; and affinis, affinity). 



(a) The first ten members of the series are : 



Methane (CH 4 ), 
Ethane (C 2 H ), 
Propane (C 3 H 8 ), 
Butane (C 4 H 10 ), 
Pentane (C 3 H 12 ), 



gas at 0°, 
gas at 0°, 
gas at 0°, 
boils at 1°, 
boils at 38°, 



Hexane (C 6 H 14 ), 
Heptane (C r H 16 ), 
Octane (C 8 H 18 ), 
Xonane (C 9 H 20 ), 
Decane (C 10 H 22 ), 



boils at 78°, 
boils at 98°, 
boils at 125°, 
boils at 148°, 
boils at 168°. 



These and many more of the series have been isolated from petroleum. 

(b) Each of the members of this series differs from its immediate 
neighbors by CH 2 . The marsh-gas series is, therefore, an homologous 
series. 

(c) The members of this series may be considered hydrides of a 
corresponding series of univalent compound radicals, thus : 

SCHOOL CHEMISTRY 15 



226 THE FOURTH GROUP TETRADS. 



Methyl (CH 8 ), 
Ethyl (C,H,), 
Propyl (C,1I-), 
Butyl (C 4 H 9 ), 
Pentyl (C 5 H U ), 



llexyl (C 6 H n ), 
Heptyl (C r II,,), 
Octvl (C 8 II K ), 
Nonyl (C 9 H 19 ), 
Decyl<C w H 2 ;). 



The use of the Greek numerals in the nomenclature of radicals and of 
paraffins, and the corresponding number of carbon atoms in each may 
serve as a mnemonic aid. 

258. The Chemical Relations of the Paraffins. — The 

paraffins are saturated compounds, having no unsatisfied 
bonds (§ 101). They, therefore, can form no compounds 
by uniting directly with other chemical substances. Com- 
pounds can be formed only by the removal of one or more 
atoms of hydrogen to make room for other elements that 
may enter into combination by substitution in exact meas- 
ure for the hydrogen removed. CH 4 or C 2 H 6> as they 
stand, can not combine with other substances ; they have 
no unsatisfied bonds with which to hold them. But, if 
deprived of one or more atoms of hydrogen, they become 
(-CH 3 )'; (=CH 2 )» or (-C 2 HY)'; (=C 2 H 4 )", and 
acquire the power to enter into combination according to 
the chemical value of the hydrogen thus lost. The known 
compounds CH 3 C1, CH 2 C1 2 , C 2 H 5 C1, and C 2 H 4 C1 2 , illustrate 
the combining power now under consideration. 

259. Metallic Character of Hydrocarbon Radicals. — It 

will be apparent from the examples given above, that the 
compound radicals formed by removing one or more atoms 
of hydrogen from any of the saturated hydrocarbons, 
behave very much as the metals do under the same chemi- 
cal conditions. Like the metals, they form oxides, hydrox- 
ides, chlorides, nitrates, sulphates, etc. 



HYDROCARBONS IN HOMOLOGOUS SERIES. 



227 



Sodium chloride. 


Sodium nitrate, 


Sodium sulphate, 


Sodium hydroxide, 


NaCl ; 


XaX0 3 ; 


Xa 2 SO, ; 


XaOH ; 


Methyl chloride. 


Methyl nitrate, 


Methyl sulphate, 


Methyl hydroxide, 


CHgCl; 


CH 3 X0 3 ; 


(CH 3 ) 2 S0 4 ; 


CH 3 OH; 


Ethyl chloride, 


Ethyl nitrate, 


Ethyl sulphate, 


Ethyl hydroxide, 


C 2 H 5 CI; 


C 2 H 5 X0 3 ; 


(C 2 H 5 ) 2 S0 4 ; 


C 2 H 5 OH. 



Preparation of Methane. 

Experiment 197. — Into a gas-pipe retort (see Appendix, § 21) 15 or 
20 cm. long, put an intimate mixture of 3 grams of sodium acetate 
(XaC 2 H 3 2 ), 3 grams of sodium hydroxide (caustic soda, XaOH), 
and 6 grams of quicklime. Place trie retort in a stove, heat it to red- 
ness, and collect over water the gas that is evolved. 

XaC 2 H 3 2 + XaOH = CH 4 + Xa 2 C0 3 . 

The lime is added to keep the mixture from fusing, and to prevent 
the escape of carbon dioxide. 

260. Marsh-gas. — The first member of the paraffin series 
is marsh-gas (methyl hydride, hydrogen monocarbide, 
methane, CH 4 ). It occurs free in nature as a constituent 
of petroleum and as a product of the decay of vegetable 
matter confined under water. 
In warm summer weather, bub- 
bles often rise to the surface of 
stagnant pools. If the vege- 
table matter at the bottom of 
the pond is stirred, gas-bubbles 
will rise rapidly. The gas may y _-~4 :^\ " 

be collected by filling a bottle "i^ -- ""^ 

with water, tying a funnel to FlG - G5 - 

its mouth, and inverting it over the ascending bubbles. 
Of this gas, about seventy-five per cent is marsh-gas; 
the rest is chiefly carbon dioxide and nitrogen. The 




228 



THE FOURTH GROUP — TETRADS. 



carbon dioxide may be removed by agitating the mixed 
gases Avith lime-water. Marsh-gas also escapes from seams 
in some coal-mines and forms the dreaded " tire-damp " of 
the miner. Mixed with air in the right proportion and 
ignited by a spark or a lamp, it explodes with great 
violence. It also escapes in large quantities from gas- 
wells, constituting about ninety-five per cent of most 
natural gas. It is formed when wood or coal is heated 
without access of air, and is therefore one of the principal 
constituents of coal-gas. 

(«) Methane may be made from its elements by the following 
reactions: C + S 2 + heat = CS 2 . 

Fe + S + heat = FeS. 
H + CI + heat = HC1. 
FeS + 2 HC1 = FeCl, + H 2 S. 
CS 2 4- 2 H 2 S + 8 Cu + heat = 4 Cu 2 S + CH 4 . 

Beginning with CH 4 , many of the most complex hydrocarbon mole- 
cules may be built up. 



Properties of Marsh-gas. 

Experiment 198. — The levity and inflammability of CH 4 may be 
shown as in the case of hydrogen, by intro-. 
ducing a lighted taper into an inverted jar 
of it. The gas will burn at the mouth of 
the jar, and the candle-flame, as it passes 
up into it, will be extinguished. 

Experiment 199. — Fill a tall bottle of at 
least one liter capacity with warm water, 
invert it over the water-pan, and pass CH 4 
into it, until a little more than one-third 
of the water is displaced; cover the bottle 
with a towel, to exclude the light, and then 
fill the rest of the bottle with chlorine. 
Cork the bottle tightly, and shake it vigorously, to mix the gases 




HYDROCARBONS IX HOMOLOGOUS SERIES. 229 

together, keeping the bottle covered with the towel. Theu open tlie 
bottle and apply a flame to the mixture. Hydrochloric acid will be 
produced, and the sides and mouth of the bottle will become coated 
with solid carbon in the form of lampblack. Test for hydrochloric 
acid with moistened blue litmus-paper and with a rod wet with 
ammonia-water. 

261. Properties. — Marsh-gas is a colorless, odorless, 
tasteless gas, slightly soluble in water. It is one of the 
lightest known substances. It is combustible, burning 
with a feebly luminous flame. Its heating power is very 
great. It forms an explosive mixture with air or with 
oxygen and has been the cause of many fatal explosions 
in ill-ventilated coal-mines. When decomposed by electric 
sparks, it yields twice its volume of hydrogen. Under 
great pressure and cold, it may be condensed to a colorless 
liquid having a density of 0.415. Under ordinary atmos- 
pheric pressure, liquid methane boils at — 164°. 

262. Other Members of the Marsh-gas Series. — Ethane 
and propane are colorless gases with properties very simi- 
lar to those of methane. Butane is a liquid at about 0°. 
The immediately following members of the series are 
liquids, but those of highest carbon contents are white 
solids at ordinary temperatures. These latter constitute 
the paraffin derived from petroleum. 

263. The Olefines. — The members of the ethylene series 
(C W H 2 „) are called olefines. Methylene (CH 2 ) has not 
been isolated. The next two members of the series, ethy- 
lene (defiant gas, C 2 H 4 ), and propylene (C 8 H 6 ), are color- 
less gases, similar in their physical properties to those 
just described. They and the higher members of the 



230 THE FOURTH GROUP — TETRADS. 

series have been isolated from petroleum. They burn 
with a luminous flame, and differ from the compounds of 
the marsh-gas series in that they are very active chemi- 
cally, uniting directly with many substances as bivalent 
compound radicals. 

(a) Xotice the relation between the nomenclature of these com- 
pounds and that of the univalent compound radicals mentioned in 
§ 257 0). 

Preparation of Acetylene. 

Experiment 200. — Put several lumps of calcium carbide into a gas- 
bottle (Fig. 6), and pour in alcohol enough to seal the lower end of 
the funnel-tube. Add water in very small quantities, and so as to 
regulate the flow of gas from the delivery -tube. Collect the gas over 
water. 

264. Acetylene. — Acetylene (C 2 H 2 ), the first member 
of the C n H 2 „_ 2 series, is a colorless gas found in coal-gas. 
It may be made from its elements by passing electric 
sparks between carbon terminals in an atmosphere of 
hj^drogen. It is more easily made by treating calcium 
carbide with water. 

CaC 2 + 2H 2 = C 2 H 2 + Ca(OH) 2 . 

The gas may be condensed to a liquid that boils at —83°. 
It has a peculiar odor, and is explosive when under pres- 
sure. Because of the facility with which it is prepared 
and of its intensely luminous power when properly burned, 
it is largely used as an illuminant, both on the small scale, 
as in bic} r cle lanterns, and on the large scale, for house 
and street lighting. 

265. Benzene. — Benzene (C 6 H 6 ), the first member of 
the C w H 2/? _ 6 series, is a liquid obtained from coal-tar by 



HYDROCARBONS IX HOMOLOGOUS SERIES. 231 

distillation. It is a good solvent of oils and of rubber. 
Like toluene, the next member of the series, it is largely 
used as a starting substance in the manufacture of coal-tar 
dyes (see § 309). 

(«) Benzene -is a hydrocarbon of constant composition, while ben- 
zine is a mixture of hydrocarbons derived from the distillation of 
petroleum. 

EXERCISES. 

1. Many bicycle lamps burn a gas that is produced as needed by 
water dropping upon a certain solid. Give the names of the solid 
used and of the gas produced. Write the reaction for the production 
of the gas. 

2. Explain the fact that two atoms of carbon may unite with two 
atoms, or with four atoms, or with six atoms of hydrogen. 

3. Symbolize and name ten successive members of an homologous 
series of compounds, and explain what is meant by such a series. 

4. Symbolize and name the compound radicals of the sixth, 
seventh, and eighth members of the series just named, and state the 
valence of the radicals. 

5. Write the graphic formula for ethyl hydride. 

6. What volume of hydrogen may be obtained by decomposing 
three liters of hydrogen monocarbide by electric sparks ? 

7. What descriptive term is applied to a series of chemical com- 
pounds having CH 2 as its increment of composition? 

8. Butylene is the fourth member of the olefine series. What is 
its formula ? 

9. What is meant by the statement that acetylene is endothermic? 

10. Put a small quantity of sodium sulphite into the gas-bottle, 
add hydrochloric acid in small quantities, collect the evolved gas by 
dry downward displacement, and test it with a burning taper and 
(very carefully) for odor. Write the equation for the reaction that 
evolved the gas. 

11. Allylene is the second member of the acetylene series. What 
is its formula? 

12. Toluene is the second member of the benzene series. Write 
its formula. 

13. Xylene is the third member of the benzene series. What is its 
formula ? 



232 THE FOURTH GROUP — TETRADS. 

14. When ordinary alcohol (C 2 H 6 0) is heated with sulphuric acid, 
the acid abstracts the elements of water from the alcohol, leaving a 
hydrocarbon gas of the C„H 2w series. Give the name and formula 
for this gas. 

15. What weight of carbon dioxide is formed by the burning of a 
liter of marsh-gas ? 

V. ILLUMINATING-GASES. 

266. Luminosity of Flames. — Flame is a phenomenon 
of burning gas ; in general, what we call flame is a gas 
combining with oxygen. It is a matter of common ob- 
servation that flames differ in their power to emit light, 
i.e., in their luminosity. For instance, the hydrogen 
flame gives practically no light, while the acetylene flame 
is intensely luminous. A solid substance in a non-lumi- 
nous flame, like a spiral of platinum wire in a hydrogen 
flame, or a bit of lime in an oxyhydrogen flame, or a Wels- 
bach mantle in a natural-gas flame, becomes luminous. 
Similarly, particles of unburned carbon in ordinary gas- 
flames make them luminous, as in the case of the acetylene 
flame or the flame of a "rich" coal-gas. In each instance, 
the light is due to the incandescence of a solid. 

(a) The illuminating power of a gas is generally expressed in 
terms of candles. For instance, the statement that a certain product 
is of eighteen candle-power means that a jet of the gas in question 
burning at the rate of five cubic feet an hour gives eighteen times as 
much light as a standard candle, i.e., a spermaceti candle that burns 
at the rate of 120 grains an hour. 

267. Illuminating-gases. — The four kinds of illumi- 
nating-gas in most common use are coal-gas, water-gas, 
natural gas, and acetylene. 

Experiment 201. — In a gas-flame heat some fine wood-shavings 
contained in a dry test-tube fitted with a cork and a short glass 



ILLUMINATING-GASES. 



233 



delivery-tube drawn out to a jet. Notice the appearance of moisture. 
Ignite the gas evolved as it issues from the apparatus. When gas 
is no longer given off, notice the residual charcoal and the tarry- 
liquid formed by this dry or destructive distillation of the wood. 

Experiment 202. — Into a gas-pipe retort, put some fragments of 
bituminous (soft) coal. To the delivery-tube, attach a piece of glass 
tubing drawn out to a jet. Place the retort in a hot fire, and, as the 
illuminating-gas is delivered, ignite it at the jet. 

Experiment 203. — Heat some pieces of bituminous coal in the gas- 
pipe or other retort and pass the gas as it is evolved through the 
apparatus shown in Fig. 67. 
The volatile liquid products 
will condense in the receiver, 
m, or " hydraulic main." 
Thence, the gaspassesthrough 
the first arm of the U-tube 
and changes the color of a 
moistened strip of red litmus- 
paper to blue, thus showing 
the presence of ammonia. In the second arm, it is tested for hydro- 
gen sulphide. In the bend of the second tube, is placed lime-water, 
which becomes milky, thus showing 
the presence of carbon dioxide . The 
gas is then collected over water. By- 
lowering the capped receiver into the 
water or by pouring more w T ater into 
the water-bath and opening the stop- 
cock, the gas may be forced out and 
burned as it issues. 




Fig. 67. 




268. Coal-gas.— Illuminat- 
ing-gases are sometimes pre- 
pared by distilling substances 
consisting in whole or in part 
of hydrogen and carbon. For 
this purpose, wood, resin, or 
petroleum is sometimes used, but, more commonly, a mix- 



234 THE FOURTH GROUP — TETRADS. 

ture of cannel and caking bituminous coals furnishes the 
desired products. A sectional view of the apparatus used 
is shown in Fig. 68. The coal is placed in Q -shaped 
retorts, six or seven feet long made of fire clay. The 
charge is about 200 pounds of coal to each retort. The 
retorts, C, are arranged in groups or " benches " of from 
three to seven. All the retorts of a bench are heated to 
a temperature of about 1200° by a single coke fire. After 
charging the retorts, their mouths are quickly closed by 
heavy iron plates. 

(a) The products of the distillation, when cooled to the ordinary 
temperature, are solid, liquid, and gaseous. 

(/;) The solid products are coke and gas-carbon. The coke is 
coal 'from which the volatile constituents have been removed by 
intense heat. It bears about the same relation to coal that charcoal 
does to w T ood. It is largely used as a fuel for domestic, metallurgical, 
and other purposes. The gas-carbon is an incrustation that gradu- 
ally forms on the inside of the retorts. It is used for making plates 
for galvanic batteries and " carbons " for arc electric lamps. 

(c) The liquid portion of the distillate is chiefly an aqueous solu- 
tion of ammonium compounds, and a viscous coal-tar that is complex 
in its composition. The coal-tar is a prolific source of carbon com- 
pounds. Among the hydrocarbons obtained from coal-tar are ben- 
zene (C 6 H r> ), toluene (C-H 8 ), xylene (C 8 H 1C ), naphthalene (C 10 H 8 ), and 
anthracene (C 14 H 10 ). 

(d) The chief constituents of coal-gas are hydrogen and marsh- 
gas, the two making about 80 per cent of the whole volume. There 
is also about 6 per cent of carbon monoxide. The remainder of 

. the coal-gas consists of small quantities of a large number of 'gases, 
including ethelyne, acetylene, nitrogen, oxygen, carbon dioxide, sul- 
phurous oxide, hydrogen sulphide, carbon di sulphide, ammonia, and 
water. 

(/?') When the volatile products leave the retort, they pass up 
through the ascension pipes, i, down the dip pipes, and bubble through 
the seal of tar and water already collected in the long, horizontal 
iron tube, mm, called the hydraulic main. From this point forward, 



ILLUMIXATIXG-GASES. 



235 



cooling ensues, accompanied by the condensation of vapors and the 
falling of the tar particles mechanically carried along in the hot rush 
of the gas from the retorts. 




236 THE FOURTH GROUP — TETRADS. 

( /') From the hydraulic main, where it leaves much of its tar and 
water, the gas passes through the vertical cooling pipes, D, called the 
condensers. Here it is cooled to 20° or 25° and largely treed from its 
tar, oils, and ammonium compounds. In large gas-works, there are 
many sets of these condensers, each set measuring several hundred 
linear feet. Every particle of gas has to pass the whole length of one 
of these sets of condensers. 

(//) In large works, an " exhauster " is placed between the hydraulic 
main and the condensers. By this means, the gas is pumped from the 
retorts and forced through the condensers, thus reducing the pressure 
in the retorts. 

(h) Chief among the impurities still remaining, are ammonium 
compounds, carbon dioxide, and hydrogen sulphide. The ammonium 
compounds are easily soluble in water. Therefore, the gas is next 
washed in the tower or " scrubber," O. Here the gas, in a finely 
divided state, rises through a shower of minute particles of water 
and, thus, has its easily soluble impurities washed out by the spray. 
To prevent the ascent of the gas in large bubbles, of which only the 
surfaces would come into contact with the water, the scrubber is filled 
with coke, brush, or lattice work for breaking up both gas and water 
into minute particles. This scrubbing aNo cools the gas still more 
and removes some of the dioxide and sulphide. The tower is generally 
three or four feet in diameter and thirty or forty feet high. More 
than one are used in some works. 

(i) The gas next passes through the purifiers, M, the object of 
which is to remove the remaining carbon dioxide and hydrogen 
sulphide. The purifier consists of boxes containing trays with per- 
forated bottoms. These trays contain the material that removes the 
impurities as the gas filters through, namely, a mixture of copperas 
(iron sulphate, FeS0 4 ) or of iron oxide, sawdust, and slacked lime. At 
manufacturing establishments where iron and steel articles are polished, 
the grindstone dust is intimately mixed with minute particles of the 
metal. This inexpensive mixture is sometimes used in the purifiers. 

(/) From the purifiers, the gas is conducted to the gas-holders, G. 
These gas-holders are sometimes 60 feet high and more than 100 
feet in diameter. 

(k) The gas, as delivered to the consumer, consists chiefly of the 
three diluents mentioned above, the marsh-gas constituting about a 
third of the gas sold. These feebly luminous gases, hydrogen, carbon 
monoxide, and marsh-gas serve as carriers of the 6 or 7 per cent 



ILLUMLSATING-GASES. 237 

of more highly luminous constituents, while the combustion of the 
former furnishes much of the heat needed for the decomposition of 
the latter and the raising of its carbon particles to the temperature 
of incandescence. 

(/) Other conditions being the same and within certain limits, the 
higher the temperature, the greater the quantity of gas produced ; the 
lower the temperature, the richer the quality. Similarly, the longer 
the time of the charge, the greater the quantity ; the shorter the time, 
the richer the quality. A skillful mixture of grades of coal and regula- 
tion of temperature and time of charge enables the gas-engineer to vary 
the products of the chemical processes in the retort and to furnish an 
article that is satisfactory to the consumer or profitable to the manu- 
facturer, or to compromise between these conflicting interests. Coal-gas 
is generally made more luminous by mixing with it a small proportion 
of the gases made by heating petroleum to a very high temperature. 

269. Water-gas. — Water-gas is prepared by bringing 
superheated steam into contact with incandescent coal or 
coke. The steam is decomposed, and hydrogen and carbon 
monoxide are produced. 

C + H 2 = CO + H 2 . 

These products are combustible, yield a non-luminous 
flame and intense heat, and may, without further prepara- 
tion, be used for heating purposes. Of course, the supply 
of atmospheric ox} T gen in the generators must be cut off to 
prevent the combustion of the mixed product. Generally, 
hydrogen sulphide and other gases are also formed from 
impurities in the coal. By enriching water-gas with a gas 
made by highly heating petroleum or other cheap hydro- 
carbons, the gas-flame is rendered luminous. Water-gas, 
thus enriched, is now used as an illuminating-gas^ but, 
owing to the large proportion of carbon monoxide, it is 
held to be more dangerous in use than coal-gas. 

(a) The apparatus most commonly used for making water-gas is 
that patented by Lowe. In many of the small cities and in some of 



238 



THE FOURTH GROUP — TETRADS. 




illujsiinatixg-gases. 239 

the larger ones, the process is used for making illuminating-gas. The 
apparatus for this method of making illuminating-gas consists of a 
boiler for generating the steam, a blower. A, for forcing air through 
the coke fire, a generator. B, where the coke is burned and gasified by 
the steam, the two chambers, C and D, where the petroleum added for 
making the gas luminous is heated so hot that it is converted into a 
permanent gas, and the chambers, E, F, and G, where the gas is 
purified. 

(ft) The process consists in blowing air and steam alternately 
through the thick bed of coke in B. The reaction between the coke 
and the steam whereby the water-gas is produced absorbs heat, so that 
during the steam-blow the generator gets colder and colder. If the 
steam-blow was continued too long, the coke would become so cold 
that the reaction would cease. The steam is, therefore, blown through 
B only four or five minutes at a time, and is then replaced by a blast 
of air from the blower, A, for about the same length of time. This 
air-blast burns coke to carbon monoxide, the reaction producing heat 
enough to make the. remaining coke bright red. The hot monoxide, 
with all the nitrogen of the air that was blown in, passes up through the 
bed of coke and over into the chamber, C, at the top of which it meets 
enough fresh air to burn about half of the CO to C0 2 . The heat 
generated by this reaction makes bright red-hot the loose brickwork 
with which C and D are filled. The carbon dioxide made in C, with 
the nitrogen from the air and the unburned portion of the carbon 
monoxide from B, pass down through the checkered brickwork in C 
and thence to the bottom of D. Here they meet a second draft of air 
just sufficient to burn the remaining CO to C0 2 . The heat from this 
combustion makes the brick in this chamber also bright red-hot. The 
exhausted nitrogen and the products of combustion pass up and out 
through the flue, H. After this heating process has been continued 
for four or five minutes, or until the attendant decides that the ap- 
paratus is hot enough, the air from the blower is cut off, the valve at 
the top of D connecting that chamber with the flue, H, is closed, the 
valve between D and the trap, E, is opened, and steam is blown in 
either at the top or bottom of the generator, B. Passing through the 
bed of hot coke, the steam is converted into hydrogen and carbon 
monoxide. These gases pass over into the chamber, C, at the top of 
which they meet a spray of petroleum. In passing down through the 
heated brickwork of C and up through that of D, the petroleum that 
is carried along by the hydrogen and the carbon monoxide is changed 



240 THE FOURTH GROUP — TETRADS. 

by the intense heat into a permanent gas of high luminous and heat- 
ing value. From D, the gaseous products pass down into the tar trap, 
E, and through the purifying apparatus, F and G. The water-gas is 
then ready for distribution. 

270. Natural Gas. — At many places, especially in pe- 
troleum-producing regions, subterranean accumulations of 
combustible gases have been found. Just as the natural 
gas from volcanic vents is characterized by a great pre- 
ponderance of carbon dioxide, so the natural gas in ques- 
tion is characterized by a great preponderance of the first 
four members of the marsh-gas series. Borings into the 
earth's crust often penetrate to these accumulations and 
allow the pent-up gases to escape from the pressure to 
which they had been subjected. This pressure is some- 
times high enough to make possible the easy transporta- 
tion of the gas through pipe-lines to great distances. 
Natural gas has come into prominence in the United 
States and Canada within the last few years as an illumi- 
nant and fuel. It consists almost wholly of methane and, 
volume for volume, has the highest heating value of any of 

the commercial gases. 

EXERCISES. 

1. Read the following symbols, thus : N 2 represents one molecule 
of nitrogen consisting of two atoms : O, 2 , 3 , H 2 0, 2H 2 0, II 2 , COa, 
CO, Cl 2 , NH 8 . 

2. Write down the weights represented by each of the following- 
expressions : 2KgO, 10H 2 O, 12CH 4 . 

3. Name the compounds symbolized as follows : CaO, MgO, KG, 
NaBr, HI, KCN. 

4. If two volumes of C 2 H 4 and four of CI are mixed, a black 
smoke and hydrochloric acid are formed. Write the reaction. 

5. How much NH3 will just neutralize 10 grams of HC1 V 

6. How many liters of oxygen are necessary to combine (complete 
combustion) with 12 grams of carbon ? 



SOME DERIVATIVES OF THE HYDROCARBONS. 2Jrl 

7. How many liters ^of chlorine are necessary to decompose 12 
liters of hydriodic acid ? 

8. (a) Distinguish between the properties of CO and those of 
CO-2- (b) How does each destroy life ? (c) Give a test f or each . 

9. Steam and chlorine are passed through a porcelain tube heated 
to redness. What takes place ? 

10. (a) What is meant by the basicity of an acid? (b) By the 
acidity of a base ? (c) How is the name of a salt derived from that 
of an acid? 

11. Write the reaction for the decomposition of steam in the 
manufacture of water-gas. 

VI. SOME DERIVATIVES OF THE HYDROCARBONS. 

271. Chloroform and Iodoform. — Many carbon com- 
pounds may be considered and classified as derivatives 
of the hydrocarbons, formed by the substitution of other 
elements or of compound radicals for one or more of the 
hydrogen atoms of the hydrocarbon. The simplest of 
these cases are those in which some of the hydrogen 
atoms are replaced by halogens. When chlorine acts on 
methyl hydride, the hydrogen of the latter is gradually 
replaced, the successive products being CH 3 C1, CH 2 C1 2 , 
CHC1 3 , and CC1 4 . Commercially, the most important 
of these halogen substitution-products are chloroform 
(CHC1 3 ) and iodoform (CHI 3 ). Both of these com- 
pounds are used in medicine and surgery. 

(a) Chloroform may be considered as methane in each molecule of 
which three atoms of hydrogen have been replaced by three atoms of 
chlorine. It is a heavy, colorless liquid of pleasant odor. When 
continuously inhaled, it produces ausesthesis. 

Marsh-gas. Chloroform. 

H H 

I I 

H — C — H CI — C — CI 

I I 

H CI 

SCHOOL CHEMISTRY — 16 



242 THE FOURTH GROUP — TETRADS. 

(b) Similarly, iodoform may be considered as methane in each 
molecule of which three atoms of hydrogen have been replaced by 
three atoms of iodine. It is a yellow solid, having a characteristic, 
disagreeable odor. 

272. The Alcohols. — When an atom of the hydrogen in 
the hydrocarbon molecule is replaced by the radical hydroxyl 
(OH), a class of compounds called alcohols is produced. 
The term "alcohol" is generally applied to the characteristic 
product of the fermentation of sugar, but in chemistry it 
is applied to a large class of bodies. 

(a) The molecular formula of an alcohol may be built up as above 
indicated by substituting the radical, OH, for an atom of hydrogen in 
the formula of a hydrocarbon molecule, or by substituting a hydro- 
carbon radical for an atom of hydrogen in the formula of water. In 
either case, it will appear that an alcohol is a hydroxide of an univa- 
lent hydrocarbon radical. This will appear more clearly in some of 
the illustrations given below. 

273. Methyl Alcohol. — The simplest and one of the 

most important of the alcohols is called methyl alcohol 
(CH 4 or CH 3 OH). It is also called wood-spirit, be- 
cause it is made by the distillation of wood. 

{a) By substituting the radical hydroxyl (OH) for hydrogen in 
marsh-gas, we have, 

Methane. Methyl alcohol. 

H H 

I I 

H — C — H. H — C — O — H. 

I I 

H II 

By substituting the radical methyl (CH 3 ) for hydrogen in water, 

we have, 

Water. Methyl alcohol. 

H — O — H, II 

I 



cn, ) , 



H > ^ II — C — O — II, or S 3 [0. 



II 



SOME DERIVATIVES OF THE HYDROCARBONS. 243 

274. Properties. — Methyl alcohol is a mobile, colorless 
liquid. When pure, its odor is pleasant, but usually the 
odor is penetrating and disagreeable. Its taste is burning 
and nauseous. It unites with water and alcohol in all pro- 
portions, burns with a feebly luminous flame, boils at about 
55°, and has a density of 0.8. It is a solvent of many 
resinous matters. 



275. Uses. — On account of its solvent powers, methyl 
alcohol is used in the preparation of varnishes. It is used 
instead of common alcohol for heating purposes. It is now 
largely used in the manufacture of aniline colors. In 
Great Britain, common alcohol containing about ten per 
cent of methyl alcohol is sold free of duty. This mixture 
is called methylated spirits, and is unfit for use as a 
beverage. 

Common Alcohol. 

Experiment 204. — Pour half of the fermented liquid of Experi- 
ment 189 into a flask, F, placed on the ring of a retort-stand. Connect 
F with an empty flask 
or bottle, b, having a 
capacity of about 100 
cu. cm., and placed in a 
water-bath. Connect b 
with a flask or bottle, c, 
immersed in cold water. 
Boil the liquid in F; 
the vapors of alcohol 
and of water pass into 
b, the temperature of 
which is a little below the 
boiling-point of water 
because its water-bath 

is kept barely boiling. Here, most of the steam is condensed while 
the alcohol vapor passes on to c, and is there condensed. The 




2U 



THE FOURTH GROUP — TETRADS. 




distillate condensed in c is dilute alcohol. If it is not strong enough 

to burn when a flame is brought 
into contact with it, it may be 
distilled again, or a second bottle 
and water-bath, b', may be inter- 
posed between b and c. The ex- 
periment should not be continued 
after a quarter of the liquid in 
F has been vaporized. Instead 
of condensing the alcohol in the 
flask, c, the Liebig condenser, 
shown in Fig. 72, may be used. 
Some water will remain in the 
alcohol even after redistillation. 
This may be removed by quick- 
lime. 

276. Ethyl Alcohol. — Common alcohol or spirits of 
wine (C 2 H 6 or C 2 H 5 OH) is formed by the fermentation 
of any liquid that contains sugar. When the juices of 
plants and fruits that contain sugar, e.g., the juice of the 
grape or the apple, stand for some time in a warm place, 
they begin to ferment. The fermentation may be caused 
by the action of yeast. The fermented liquid lacks the 
sweet taste of the sugar because the sugar (C 6 H 12 6 ) has 
been decomposed into carbon dioxide and alcohol. 
C 6 H 12 6 =2C a H 6 0+2C0 2 . 

(a) We have here a good illustration of the facility with which 
carbon atoms unite themselves one to another and thus constitute the 
framework of various hydrocarbon molecules. For example, we have 
H 



the methane molecule, H — C — H. Bv replacing one atom of this hy- 
I H II 

H I | 

drogen with the univalent radical methyl (C H 8 ), we have II — C — C — H 

H H 



SOME DERIVATIVES OF THE HYDROCARBONS. 245 

or ethane (ethyl hydride). By substituting the univalent radical, HO, 

H H 
I I 
for one atom of the hydrogen in ethane, we have (HO) — C — C — H, or 

I I 
H H 
ordinary alcohol (ethyl hydroxide). By successive substitutions of 
(CH 3 )' for H, we may pass from CH 4 to C 2 H 6 , C 3 H 8 , C 4 H 10 , or 
H H H H 
I I I I 
H — C — C — C — C — H, etc. 
I I I I 
H H H H 

277. Distilled and Fermented Liquors. — By the action 
of a substance called diastase, formed in barley and other 
grains during germination, starch is converted into sugar. 
Great quantities of starch are thus converted into sugar 
for the manufacture of alcohol. In Europe, the cheapest 
source of the starch used for this purpose is the potato ; 
in the United States, the starch of Indian corn is more 
commonly used. The maize is ground, heated with steam 
until disintegrated, cooled, mixed with germinated barley 
(i.e., malt), and allowed to stand until the starch is con- 
verted into sugar. Yeast is then added and the liquid 
allowed to ferment until the sugar is converted into 
alcohol. The resulting liquid is then distilled, the dis- 
tillate being whisky. A second or third distillation 
produces nearly pure alcohol. Beer is made in a some- 
what similar manner from malt, hops, and water without 
distillation. Wine is made by the fermentation of fruit 
juices. The distillation of wine yields brandy. 

(a) A great deal of alcohol is made by the fermentation of the 
refuse molasses of sugar manufacture. Beer generally contains from 
4 to 6 per cent of alcohol ; wine, from 10 to 20 per cent ; and brandy 
and whisky, about 50 per cent. 



246 THE FOURTH GROUP — TETRADS. 

278. Fermentation. — The change of sugar into alcohol is 
caused b} r minute organized bodies that grow in the solution 
of sugar and feed upon it. When properly fed and kept 
at a temperature of about 20°, these organisms increase 
with great rapidity. They are a species of plants and 
the chief products of their growth are carbon dioxide 
and alcohol. The germs or seeds of the yeast-plant are 
generally present in the air so that when a liquid suitable 
to their growth is exposed to the air under favorable con- 
ditions of temperature, the growth of the germs is sure to 
begin. This is why fruit juices that contain sugar may 
be changed to alcohol without the addition of yeast. This 
process whereby chemical changes are effected by the growth 
of minute organisms is called fermentation. 

(a) There are many kinds of fermentation, each caused by the 
growth of a special organism or ferment. That caused by the yeast- 
plant is called the alcoholic fermentation. The souring of milk is 
caused by another organism called the lactic ferment; such changes 
are called lactic fermentation. Another organism feeds upon the 
alcohol produced by the yeast-plant and converts it into acetic acid, so 
that, under suitable conditions of temperature and exposure, sugar 
solutions ultimately become sour and are converted into vinegar as 
will soon be explained more fully. Still other organisms cause the 
decay of nitrogenous organic substances — the putrefactive fermenta- 
tion. 

(b) In general, these ferments tend to break up complex into 
simpler chemical compounds, to convert the carbon compounds of 
organized nature back to the final oxidation products, water and 
carbon dioxide. 

(c) When the growth of the ferments is prevented, decay ceases; 
substances may thus be preserved indefinitely. Most of the ferments 
are killed by long boiling; a few kinds require a higher temperature. 
In canning fruits and vegetables, the ferments are destroyed by heat, 
and the access of other germs from the air is prevented by sealing the 
hot liquid in cans. If air is admitted after the contents of the can 



SOME DERIVATIVES OF THE HYDROCARBONS. 24:7 

are cool, the ferments enter with the air, growth begins, and the fruit 
is spoiled. A similar result is secured in embalming processes, the 
ferments being destroyed by poisons, such as arsenic and corrosive 
sublimate. 

279. Properties of Alcohol. — Alcohol is a colorless, vola- 
tile, inflammable liquid. It is about four-fifths as heavy 
as water ; its boiling-point is 78° ; it remains liquid at 
very low temperatures, but freezes at about —130°. It 
absorbs moisture from the atmosphere, and is capable of 
mixing with water in all proportions. Alcohol that con- 
tains no water is called absolute alcohol. The strength 
of alcohol is generally spoken of by its percentage of 
"proof -spirits." Proof -spirit is of such a strength that it 
will just burn ; it contains forty-nine per cent of absolute 
alcohol and fifty-one per cent of water. 

280. The Physiological Action of Alcohol. — Concen- 
trated alcohol is an active poison ; diluted alcohol taken 
in large quantities has caused death. As alcohol is partly 
oxidized in the animal system, it furnishes some heat, but 
its physiological action is so much more important than 
its heating value that the temperature of the body is 
usually lowered by its use. The prolonged use of alco- 
holic beverages is accompanied by general degenerative 
changes that usually result in enfeebled vital organs, 
especially the heart and liver. Alcohol should undoubt- 
edly be classed as a poisonous drug and not as a food. 
The evil effects of its excessive use are everywhere 
apparent. 

281. Uses of Alcohol. — Alcohol is largely used in the 
chemical laboratory, in pharmacy, and in the arts. It 



248 THE FOURTH GROUP — TETRADS. 

affords a smokeless fuel and is an indispensable solvent 
for many substances (such as resins and oils) that are 
insoluble in water. It is largely used in the preparation 
of varnishes, perfumes, and medicinal tinctures, and is 
the fundamental principle of all fermented and distilled 
liquors. 

282. Other Alcohols. — Most of the alcohols that con- 
tain a greater number of carbon atoms to the molecule 
than does ethyl alcohol are of little commercial impor- 
tance, glycerine being the chief exception. Most of them 
are liquids that increase in density and in temperature of 
boiling with the increase in the number of carbon atoms. 
The highest in the series are solids. 

283. Ethers. — As the abstraction of water from the 
hydroxides of the metals yields metallic oxides, so does 
the abstraction of water from the alcohols, which" are 
hydroxides of the univalent carbon radicals, yield oxides 
that are called ethers. Thus methyl alcohol yields methyl 
ether, and ethyl alcohol yields ethyl ether. 

2CH 3 OH = (CH 3 ) - O - (CH 3 ) + H 2 0. 

2C 2 H 5 OH = (C 2 H 5 ) - O - (C 2 H 5 ) + H 2 0. 

This abstraction of water is most readily effected by treat- 
ment of the alcohol with strong sulphuric acid. 

284. Common Ether. — Ether [" sulphuric ether," ethyl 
ether, ethyl oxide (C 2 H 5 ) 2 0] is prepared by distilling a 
mixture of strong sulphuric acid and alcohol. The distil- 
late, which is a mixture of ether and water, is condensed 
in a cold receiver and separates into two layers, water 



SOME DERIVATIVES OF THE HYDROCARBONS. 249 

below and ether above. The ether is drawn off and wholly 
freed from water by allowing it to stand over quicklime, 
and then redistilling it. 

Properties of Ether. 

Caution. — Owing to the danger arising from the extreme vola- 
tility and inflammability of ether, the pupil should deal with only 
minute quantities of this compound. 

Experiment 205. — Put 10 or 12 drops of common alcohol and an 
equal quantity of sulphuric acid into a test-tube and heat gently. 
The peculiar odor of ether may be recognized. 

Experiment 206. — Pour a small quantity of ether into the palm of the 
hand aud notice its rapid evaporation and absorption of sensible heat. 

Experiment 207. — Put a few drops of ether into a tumbler, cover 
loosely and, after the lapse of a minute, bring a flame to the edge of 
the tumbler. The heavy ether vapor will ignite with a sudden flash. 

285. Properties. — Ether is a colorless, volatile, inflam- 
mable liquid, having a density of 0.72. It is almost 
insoluble in water and has a strong and peculiar odor. 
It is largely used as an anaesthetic in surgical operations. 
Its common name, "sulphuric ether," comes from the 
method of its preparation, and is a misnomer ; ether 
contains no sulphur. 

Note. — The relations of C 2 H 6 and (C 2 H 5 ) 2 to each other and 
to their common compound radical, ethyl, may be made more evident 
by the following typical formulas : 

Water type. Alcohol. Ether. - t 

R$ Hj U (C 2 H 5 )'} U 

Aldehyde. 

Experiment 208. — Place a few pieces of potassium dichromate (a 
good oxidizing agent) in a small flask and pour upon it a few cubic 
centimeters of strong sulphuric acid. Then add slowly a like quan- 
tity of ordinary alcohol aud notice the odor. 



250 THE FOURTH GROUP — TETRADS. 

286. Aldehydes. — This is the general name of a class 
of compounds intermediate between the alcohols and the 
hydrocarbon acids. They are derived from their corre- 
sponding primary alcohols by the oxidation and removal 
of two atoms of hydrogen, as is signified by the etymology 
of the name. By the addition of an atom of oxygen, an 
aldehyde is converted into an acid. 

287. Formic Aldehyde. — Formic aldehyde (CH 2 or 
H — C^tt) is made by oxidizing methyl alcohol. 

2CH 4 + 2 = 2CH 2 + 2H 2 0. 

Its solution in water is called formalin. Formalin is a 
powerful and useful disinfectant. 

288. Acetic Aldehyde. — Acetic aldehyde (ordinary al- 
dehyde, ethaldehyde, acetaldehyde, C 2 H 4 0) is produced 
by the oxidation of ordinary alcohol (i.e., ethyl alcohol). 

C 2 H 6 + O = C 2 H 4 + H 2 0. 

It is a volatile liquid with a characteristic pungent odor. 
It is easily converted into paraldehyde, a substance of the 
same percentage composition. Paraldehyde is used in 
medicine ; its vapor-density shows (§ 134) that it is 
represented by the formula, C 6 H 12 3 . 

289. Chloral. — Chloral (C 2 C1 3 H0) is a colorless liquid 
formed by the action of chlorine upon alcohol. With 
water it forms chloral hydrate (C 2 C1 3 H0, H 2 C)), an easily 
soluble crystalline compound used in medicine. Just as 
chloroform may be regarded as a trichlorine substitution 






SOME DERIVATIVES OF THE HYDROCARBONS. 251 

product derived from marsh-gas, so chloral may be re- 
garded as a like product derived from aldehyde. 

290. Hydrocarbon Acids. — When one or more of the 
hydrogen atoms of a hydrocarbon molecule are replaced by 

//° 

the hypothetical compound radical carboxyl ( — C ), 

NO— H 
an acid is produced. As only the hydrogen of the car- 
boxyl is replaceable by a basic element or group, the 
basicity of the acid depends upon the number of these 
carboxyl groups. 

291. Formic Acid. — This acid (CH 2 2 ) is of greater 
theoretical than commercial importance. It is a colorless 
liquid and occurs in nature in red ants (whence its name), 
in stinging nettles, and elsewhere. It may be regarded 
as formic aldehyde (CH 2 0) to which an atom of oxygen 
has been added (§ 286), or as a compound of hydrogen 
and carboxyl (H — COOH). It is the first member of an 
homologous series called fatty acids, having the general 
formula C w H 2re 2 . 

292. Acetic Acid. — This acid (" pyroligneous acid," 
wood vinegar, C 2 H 4 2 ), when pure, is a colorless liquid 
having a penetrating odor and an intense acid taste. It 
is extremely corrosive, causing blisters when brought into 
contact with the skin. In its pure state, at temperatures 
below 16°, it is a crystalline solid, known as glacial or 
crystalline acetic acid. Acetic acid is the second mem- 
ber of the series of fatty acids, and may be regarded 
as acetic aldehyde to which one atom of oxygen has 



252 THE FOURTH GROUP — TETRADS. 

bden aided (§ 286), or methane in which one hydrogen 
atom has been replaced by carboxyl (§ 290). 
H 

I /y o 

H— C— Cf 

| V)— H. 
H 

As it has only one replaceable hydrogen atom, viz., the 
one in the group CO OH, the acid is monobasic. It is 
this acid that gives the sour taste and peculiar odor to 
vinegar. Vinegar is a dilute solution of acetic acid with 
coloring matter and other soluble impurities derived from 
the juice of the fruit from which it is generally made. 

(a) If the remaining part of the fermented liquid of Experiment 
180 has stood a few days, it may be found to have a sour taste. If it 
stands long enough, it will be changed to vinegar. By oxidation, the 
alcohol is changed to acetic acid and water, two hydrogen atoms of 
the alcohol being replaced by one oxygen atom. 

Alcohol. Acetic acid. 

CH 3 — C< + O, = CH,— Cf + HoO. 
X)H " X)H 

(7>) Large quantities of acetic acid are also obtained by the destruc- 
tive distillation of wood in large iron retorts. The liquid portion of 
the distillate is made, by further treatment, to yield acetic acid. This 
method of preparation is the origin of the alternative names above 
recorded. 

293. Acetates. — Acetic acid forms a very large and 
important class of salts called acetates. Lead acetate 
[Pb(C 2 H 3 2 ) 2 ], unfortunately called sugar of lead 
because it is sweet, is a dangerous poison used in medi- 
cine. Another well-known salt of acetic acid is copper 
acetate [Cu(C 2 H 3 2 ) 2 ], a variety of which is called ver- 
digris. 



SOME DERIVATIVES OF THE HYDROCARBONS. 253 

294. Vinegar. — Vinegar may be made by allowing 
wine or cider or some dilute alcohol mixed with a little 
old vinegar to stand in casks with free access of air. 
The alcohol, under the influence of a peculiar ferment, 
takes up oxygen, changing first to aldehyde and after- 
ward to acetic acid. By this mode, only a small surface 
is exposed for oxidation, perhaps one square yard to one 
hundred gallons. The process will, therefore, be slow. 
If the same volume of the liquid is exposed in wide, shal- 
low vessels, the oxidation will be more rapid. It will be 
still better to allow the liquid to trickle over shavings 
placed in a vessel that allows a free access of air to its 
interior, giving a surface of exposure of one hundred 
square yards to a gallon of liquid. The process of oxida- 
tion will then go on more rapidly. Vinegar of excellent 
quality may be thus prepared in a few hours. The pro- 
cess would otherwise require months. 



(a) Figure 73 
shows the plan of a 
vessel, AB. About 
a foot from the top 
is a disk, b b, per- 
forated with holes 
one-quarter inch in 
diameter and about 
an inch apart. Into 
these holes cotton 
wicks, knotted at the 
top, are placed to 
conduct the liquid 
at a proper rate to 
the space below. 
Near the bottom an- 
other perforated disk 




254 THE FOURTH GROUP — TETRADS. 

is placed. Between these disks the vessal is filled with shavings, upon 
which the liquid from the space above trickles. Oxidizing air is ad- 
mitted through holes in the side of the vessel and passes upward, escap- 
ing through the tubes or chimneys, a a, as shown by the arrows. Old 
vinegar is first allowed to trickle over the shavings until a gelatinous 
coating is formed upon them. This coating acts as a ferment. Char- 
coal in pieces as large as a walnut is said to be better than shavings, 
serving the double purpose of giving greater surface and of condens- 
ing the oxygen of the air in its pores, thus favoring oxidation without 
the ferment. The vinegar settles slowly to the bottom and is drawn 
off through a siphon or a stop-cock at s. 

(?>) Vinegar is also made in large quantities from dilute alcohol 
made from corn. This naturally colorless product is usually colored 
with burned sugar to give it the appearance of fruit vinegar. 

(c) The peculiar ferment known as " mother of vinegar " is a 
microscopic fungus which appears on the surface of the liquid, where 
it absorbs oxygen from the air and subsequently gives it to the alcohol. 

295. Other Fatty Acids. — The most important of the 
higher members of this C w H 2w 2 series are propionic 
acid (C 3 H 6 2 ), butyric acid (C 4 H 8 2 ), palmitic acid 
(C 16 H 32 2 ), and stearic acid (C 18 H 36 2 ). For reasons 
that will soon appear it is convenient to mention here 
a member of the C n H 2ra _ 2 2 series, namely, oleic acid 
(C 18 H 34 2 ). The principal vegetable and animal fats 
and oils are palmitates, stearates, and oleates. 

EXERCISES. 

1. Write the graphic formula for iodoform. 

2. "Write the formula for ethaldehyde and paraldehyde. What is 
the name of the law that justifies the statement that there are three 
times as many atoms in a liter of the vapor of the latter as in a liter 
of the vapor of the former? 

3. Formic acid is the first member of an homologous series of 
acids. What one word distinguishes these from other acids ? 

4. Why is acetic acid monobasic ? 

5. Write two graphic formulas showing that chloroform may be 
looked upon as a derivative from marsh-gas. 



SOME DERIVATIVES OF THE HYDROCARBONS. 2o5 

6. Symbolize the alcohols of the first five members of the paraffin 
series. 

7. What generic term is applied to the hydroxides of the hydro- 
carbon radicals ? 

8. Write two graphic formulas showing that wood-spirit may be 
looked upon («) as a derivative of marsh-gas ; (b) as a derivative of 
water. 

9. Symbolize the acetates of K, Pb", Cu", and Ca". 
10. Show that an ether is a dehydrated alcohol. 

296. Analogous Hydroxides. — Just as the hydroxide of 
an univalent hydrocarbon radical is called an alcohol, so 
the hydroxide of a bivalent hydrocarbon radical is called 
a glycol, and the hydroxide of a trivalent hydrocarbon 
radical is called a glycerol. In other words, an alcohol 
contains one hydroxyl group joined to a carbon atom, a 
glycol contains two hydroxyd groups united to different 
carbon atoms, and a gtycerol contains three hydroxyl 
groups united to three carbon atoms. 

(«) Glycols and glycerols are sometimes spoken of as more complex 
alcohols. 

297. Glycols. — In our study of the marsh-gas series, 
we have had to do with a series of univalent compound 
radicals (§ 257, c) that bore a very simple relation to 
the paraffins themselves. In the ethelyne or olefiant-gas 
series, the successive homologues may act either as satu- 
rated molecules, i.e., in the free state, or as bivalent com- 
pound radicals. 

H H H H 

II II 

C = C, or — C — C— . 

II II 

H H H H 



256 THE FOURTH GROUP — TETRADS. 

From these bivalent radicals are built up, in a now 
familiar way, series of glycols, acids, etc., many of them 
with numerous isomeric forms. As common alcohol is 
ethyl hydroxide, G 2 H 5 — OH, so ordinary glycol is ethy- 
lene dihydroxide, C 2 H 4 (OH) 2 . By this process of adding 
(OH) 2 to the formulas for the successive members of the 
ethylene series, we obtain the formulas for a series of 
glycols, analogous to the series of alcohols. 

298. Oxalic Acid. — The oxidation of the glycols gives 
a series of hydrocarbon acids, at least one member of 
which is of industrial importance. If ordinary glycol 
is gently oxidized, glycolic acid is produced. 

Glycol. Glycolic acid. 

CH 9 0H COOH 

| +0 2 = | +H 2 0. 

CH 2 OH CH 2 OH 

As the familiar carbonyl group herein appears but once, 
glycolic acid is monobasic (§ 290). If the glycol is more 
completely oxidized, oxalic acid is produced. 
Glycol. Oxalic acid. 

CH 9 OH COOH 

i +20 2 = | 

CH 2 OH COOH 

Evidently this acid, C 2 H 2 4 , is dibasic. Both of these 
acids are found in nature. Oxalic acid is an active 
poison. It is used in calico-printing, in straw-bleaching, 
in cleaning brass and other metals, in removing ink-stains 
from cloths, etc. It is prepared on the small scale by the 
action of nitric acid upon granulated sugar, and on the 
large scale by heating wood shavings or sawdust with 



SOME DERIVATIVES OF THE HYDROCARBONS. 257 

sodium and potassium hydroxides. As it forms harmless 
salts with calcium and magnesium, its best antidote is 
chalk or magnesia. If neither of these is at hand, the 
whitewash scraped from a wall may be used. 

299. Other Vegetable Acids. — Lactic acid (C 3 H 6 3 ) is 
made by the lactic fermentation of sugar (§ 278, a). 
Malic acid (C 4 H 6 5 ) occurs in many fruits, such as 
apples, cherries, etc. Tartaric acid (C 4 H 6 6 ) is widely 
distributed in fruits such as grapes, cucumbers, potatoes, 
berries of the mountain-ash, etc. It is prepared from 
argol, an acid potassium tartrate (KHC 4 H 4 6 ) that is 
deposited in crusts from fermenting wines. Purified 
argol is called cream of tartar. Tartaric acid is dibasic. 
It is largely used in dyeing, in calico-printing, and in the 
manufacture of baking-powders. Sodium-potassium tar- 
trate is called Rochelle salt. Tartar emetic is a tartrate 
of potassium and antimony. Citric acid (C 6 H 8 7 ) also 
occurs in many fruits, especially lemons, from the juice 
of which it is prepared. 

H 9 = C-0H 
I 

300. Glycerin. — Glycerin, C 3 H 5 (OH) 3 , or H - C - OH, 

I 
H 2 =C-OH 
is produced in small quantities in the fermentation of 
sugar, nearly three per cent of the products being .gl} r c- 
erin. It is also a by-product of soap -making and of the 
manufacture of stearic acid. 

(a) Glycerin may be regarded as a hydroxide of the trivalent com- 
pound radical glyceryl, C 3 H 3 . Being the hydroxide of a trivalent 
hydrocarbon radical (§ 298), it is a glycerol, an analogue of alcohol 
and glycol. 

SCHOOL CHEMISTRY — 17 



258 THE FOURTH GROUP — TETRADS. 

301. Properties of Glycerin. — Glycerin is a sweet liquid 
of syrupy consistency, and without odor or color. It is 
non-volatile under ordinary conditions. At — 40°, it 
solidifies to a fine crystalline mass. Glycerin is soluble 
in water and in alcohol in all proportions. It absorbs 
moisture from the atmosphere and ranks next to water 
as a solvent. 

302. Uses. — Glycerin is used in the manufacture of 
nitroglycerin and dynamite. On account of its oily and 
non- volatile properties, it is used as a lubricant for watch- 
and clock-work. The same properties and its antiseptic 
nature make it useful as an application to the skin to 
keep it soft and pliable and to prevent chapping. 

303. Natural Fatty Bodies. —Nearly all the fats, oils, 
and waxes of the animal and vegetable kingdoms are 
compounds of the hydrocarbon acids. The most im- 
portant of these fats and oils are palmitin, stearin, and 
olein. Palmitin and stearin predominate in the composi- 
tion of the solid fats, and olcin in that of the oils. 

(a) Palmitin, stearin, and olein may be regarded as salts formed 
by substituting the trivalent radical glyceryl (C 3 H 5 ) for three atoms 
of hydrogen in three molecules of their respective acids (§ 295). 
Thus palmitin is glyceryl palmitate [C 3 H 5 (C 16 H 31 2 ) 3 ], stearin is 
glyceryl stearate [C 3 H-(C 18 H 35 2 ) 3 ], and olein is glyceryl oleate 
[C 3 H 5 (C 18 H 33 2 ) 3 ]. 

Soap-making. 

Experiment 209. — Tn an iron pot boil for about an hour 115 grams 
(a quarter of a pound) of lard with a solution of 40 grams of caustic 
soda in 250 cu. cm. of water. When the liquid is cooled, add a strong 
solution of common salt. Soap will rise to the surface and become 
solid when cold. 



SOME DERIVATIVES OF THE HYDROCARBONS. 259 

304. Soaps. — Soaps are salts formed by the substitution 
of the alkali metals for the glyceryl in the fats, i.e., they are 
the alkali salts of the fatty acids, especially palmitic and 
stearic acids. The following shows the reaction : 

Sodium 
Stearin. hydroxide. Sodium stearate. Glycerin. 

QACCjAA). + SXaOH = 3Na(C 18 H 35 2 ) + C 3 H 5 (OH) 3 . 
Common soap may be prepared by boiling tallow in a 
weak solution of sodium hydroxide. As saponification 
proceeds, stronger solutions are to be added until all the 
grease disappears. If the fat was boiled in a strong lye 
at first, a coating of soap would be formed around it, pro- 
tecting it from further action of the lye, soap being insol- 
uble in a strong alkali solution. The soap, when formed, 
is in solution in the water and glycerin that are present. 
From this solution it may be separated by adding common 
salt to form a brine in which the soap is insoluble. The 
soap will rise and become a solid at the surface ; the glyc- 
erin will remain in solution. 

(a) Soft soap is potassium palmitate and stearate ; hard soap is 
sodium palmitate and stearate. 

Experiment 210. — Pass carbon dioxide through half a liter of dilute 
lime-water until the precipitate that is formed is dissolved. Rub a 
bit of soap between the hands wet with this hard water. 

Experiment 211. — Repeat Experiment 210, using a hard water 
made by shaking some powdered gypsum with a liter of soft water. 

305. Properties. — Soap is soluble in water or in alcohol. 
If a large quantity of water is added to a solution of soap, 
some of the soap is decomposed, setting a portion of the 
alkali free in solution and precipitating an insoluble 
acid sodium stearate in pearly scales. It is this property 



260 THE FOURTH GROUP — TETRADS. 

that renders soap useful as a cleansing agent. The large 
amount of water used decomposes the soap, the alkali 
enters into composition with the grease of the dirt, and 
renders it soluble in the water. The fatty acid is carried 
away in the lather formed. 

When soap is added to a hard water, insoluble calcium 
or magnesium salts of palmitic and stearic acids are 
formed. All of these insoluble salts must" "be precipitated 
before the soap can have any cleansing action. 

(a) Many soaps contain adulterants such as soluble silicates, resin, 
sand, pipe-clay, etc. When the genuine article can be had, Castile 
soap made of olive-oil is the best of all soaps. 

306. Saponification. — Any process by which the fatty 
acids and the glycerin are separated and set free is called 
saponification. Soap-making is but one process. Glycerin 
may be separated from the fatty acids by means of super- 
heated water, the latter behaving, at a high temperature, 
much as do the alkalies. 

Stearin. Water. Stearic acid. Glycerin. 

( C 18 H 35°)3? n _L_ H 3?r> ( C 1S H 35°)3? , C 3 H 5 ? 

c 3 hJ° 3+ hj U3 - Hj 3+ H 3 r^ 

307. Common Fats. — The common fats are mixtures of 
the natural fats mentioned above. Tallow is composed 
mostly of stearin. Olein predominates in lard. Butter 
is distinguished from the other fats by containing butyrin, 
the glycerin salt of butyric acid. It is to this salt that 
the pleasant odor and flavor of fresh butter are due. In 
rancid butter, some of the butyric acid has been set free, 
imparting its disagreeable odor. The acid may be re- 
moved and the butter made sweet by sufficient washing 



SOME DERIVATIVES OF THE HYDROCARBONS. 261 

with water. In trade parlance, such butter is said to be 
"renovated. 5 ' When the fatty part of beef suet is sepa- 
rated from the fibrous matter and then melted in tanks 
surrounded with water of a temperature of 50°, a clear 
yellow oil is obtained. This oil is allowed to solidify, 
and is then subjected to pressure at a temperature of 
32°. From the oil that flows away, great quantities of 
artificial butter are now made. This is done by mixing 
this oil with lard and cotton-seed oil, and churning the 
mixture with milk to give it the taste and odor of true 
butter. The product is called butterine or oleomargarine, 
and differs but slightly in chemical composition from true 
butter. The stearic acid separated from fats is a white 
solid largely used in the manufacture of candles. 

308. Oils. — Oils are liquid fats that exist ready formed 
in nature. Most of them are fluid at ordinary tempera- 
tures. They are insoluble in water but completely soluble 
in ether. Most of them are only sparingly soluble in 
alcohol. Oils are classified as fixed oils and essential oils. 
The fixed oils leave a permanent stain on paper and can not 
be distilled without decomposition. They are glyceryl 
salts and form soaps with alkaline bases, as already illus- 
trated. They are grouped according to their origin, as 
vegetable oils and animal oils. The essential oils are 
volatile and not capable of saponification. 

(a) The vegetable oils occur chiefly in the seeds of plants or in 
the pulp about the seeds. They are usually divided into two groups, 
the drying oils and the non-drying oils. The drying oils, like linseed- 
oil, absorb oxygen on exposure to the air, sometimes with the evolu- 
tion of so much heat that spontaneous combustion takes place. They 
are extensively used in making varnishes and mixing paints. Castor- 



262 THE FOURTH GROUP — TETRADS. 

oil is a connecting link between the drying and the non-drying oils. 
The non-drying oils like olive- (sweet-) oil and cotton-seed oil become 
rancid on exposure to the air. 

(b) The animal oils are glyceryl salts of the fatty acids, and so 
rich in oleic acid that they remain liquid at ordinary temperatures. 
Sperm-oil, train-oil, cod liver oil, neat's-foot oil, and lard oil are 
familiar members of this group. They have a characteristic and 
persistent odor which in some of the fish oils is peculiarly offensive. 

(c) The essential or volatile oils are generally obtained by distill- 
ing the parts of plants in which they occur. They are soluble in 
alcohol or ether. Some of them, like the oils of lemon and of orange, 
are so abundant in the leaves and the skin of the fruit that they may 
be separated by mechanical pressure. Most of them are isomeric or 
polymeric with oil of turpentine (C 10 H 16 ), and absorb oxygen rapidly. 
By such absorption the oil of turpentine acquires the properties of 
ozone and often bleaches the inner end of the cork of the bottle that 
contains it. Essences are prepared from the essential oils by distil- 
lation with water or by the addition of water in sufficient quantity 
to hold the oils in emulsion. 

309. Aniline Dyes. — The fact that many hydrocarbons, 
including benzene, toluene, naphthalene, anthracene, and 
carbolic acid, are obtained from coal-tar, and that some of 
these serve as starting-points in the preparation of many 
other hydrocarbons, has already been stated (§§ 268, c, and 
265). Thus, when benzene is treated with nitric acid, the 
products of the reaction are nitrobenzene (C 6 H 5 N0 2 ) and 
water. Nitrobenzene is a yellow liquid with an odor much 
like that of oil of bitter almonds. When nitrobenzene is 
treated with a solution that yields nascent hydrogen, its 
oxygen is replaced thus : 

C 6 H 5 N0 2 + 6H = C 6 H 5 NH 2 + 2H 2 0. 

This product, C 6 H 5 NH 2 , is a colorless liquid known as 
aniline. By treating aniline and a similar substance known 
as toluidine with mercuric chloride or arsenic acid, the dye 



SOME DERIVATIVES OF THE HYDROCARBONS. 263 

called magenta is produced. Most of the aniline dyes, of 
which there are many and some of which are very beauti- 
ful, are prepared from magenta. 

310. Other Aromatic Compounds. — As many of these 
coal-tar products have a pleasant aromatic odor, they are 
often called aromatic compounds. By oxidizing toluene 
(C 7 H 8 ), which it will be remembered is found in coal-tar, 
benzoic acid (C 7 H 6 2 ) is produced. This acid also occurs 
in gum benzoin and in the balsams of Peru and Tolu. 
By the removal of an atom of oxygen from the formula 
for benzoic acid, we have the formula for the oil of bitter 
almonds (C 7 H 6 0). Thus, the oil of bitter almonds is 
benzoic aldehyde (see § 286). The oil of bitter almonds 
occurs in bitter almonds, laurel-leaves, cherry-stones, etc. 
The preparation of this " organic " compound from coal- 
tar, and its use in turn in the preparation of artificial 
indigo, constitute one of the historic victories by which 
modern chemistry broke down the ancient wall between 
organic and inorganic chemistry. 

(a) Anthracene, another constituent of coal-tar, is largely used 
in the preparation of alizarin. This well-known dye was formerly 
obtained from madder-root. Now the artificial alizarin is almost 
exclusively used for dyeing Turkey red. 

311. Carbolic Acid. — This familiar substance, sometimes 
called phenol (C 6 H 6 or C 6 H 5 OH), may be considered as 
benzene in which hydroxyl has replaced one of the hy- 
drogen atoms. It is extracted from coal-tar. It is not 
properly an acid, but it has some acid properties. It is 
extremely corrosive and poisonous, and is extensively used 
as a disinfectant. 



264 THE FOURTH GROUP — TETRADS. 

EXERCISES. 

1. Give the name and valence of C 3 H S and write its graphic 
formula. 

2. Why was salt added at the end of Experiment 209 ? 

3. What is the diiference between the composition of soft soap 
and that of hard soap? 

4. Can you detect in the name carboxyl a suggestion of the names 
of two or more simple compound radicals of which we may suppose 
that carboxyl is made up ? 

5. Propionic acid is the third member of an homologous series of 
which the first is formic acid. Write the formula for propionic acid. 
Write the general formula for the series. 

6. Give the formula and name of the eighteenth member of this 
acid series. 

7. What is the general name for the hydroxide of a trivalent 
hydrocarbon radical? 

8. By the progressive oxidation of ordinary glycol, two different 
acids are formed one of which is monobasic, the other dibasic. Give 
their names and the name of the atomic group that determines their 
basicity. 

9. Outline in succession the changes in the condition of a particle 
of carbon as it completes the cycle of a constituent of the atmos- 
phere, of vegetable matter, of animal matter, and of the atmosphere 
again. 

10. (a) How much soap may be made by the use of 10 pounds of 
pure stearin? (b) How much sodium hydroxide must be taken? 

11. How much glycerin is there in 100 kilograms of tallow, suppos- 
ing the latter to be pure stearin? 

12. Write the formula of a lead soap and of a calcium soap. 

13. When soap is dissolved in water containing CaS() 4 , a reaction 
takes place giving an insoluble calcium soap. Write the reaction. 

14. If an excess of H 2 S0 4 is added to a small quantity of CH 2 2 in 
a test-tube, and a gentle heat is applied, a regular disengagement of 
gas takes place. The gas comes from the decomposition of the fatty 
acid and burns with a blue flame. Water is formed at the same time. 
Write the reaction. 

15. (a) What is the name of CH 3 — CH 2 — CH 2 — CH 3 ? (b) Write 
its full structural formula. 

16. Show that chlorine is diatomic. 



THE CARBOHYDRATES. 265 

17. Write the reaction for the production of nitrobenzene from 
benzene. 

18. Write the reaction for the preparation of aniline from nitro- 
benzene. What peculiar condition of the gas used is necessary to the 
reaction ? 

19. From the formula for olein (glyceryl oleate) determine the 
basicity of oleic acid. Write a structural formula for oleic acid that 
shall indicate its basicity by the number of its carboxyl groups. 

20. Show by graphic formulas that a valuable disinfectant may be 
provided by oxidizing methyl hydroxide and dissolving the product 
in water. Give the name of this disinfectant. 

VII. THE CARBOHYDRATES. 

312. Carbohydrates. — The carbon compounds of this 
class include the most abundant substances found in the 
vegetable kingdom. Each of them consists of hydrogen 
and oxygen in the proportions to form water, and com- 
bined with six atoms of carbon or some multiple of six 
atoms of carbon for each molecule of the carbohydrate. 
As they enter largely into the economy of plant and 
animal organisms, they are of great physiological impor- 
tance. 

There are three general classes as follows : 

1. C 12 H 22 O n ; as sucrose. 

2. C 6 H 12 6 ; as dextrose and levulose. 

3. C 6 H 10 O 5 ; as starch, inulin, dextrin, and cellulose. 

The members of the first two groups are called sugars ; 
they are soluble in water, and are more or less sweet in 
taste. The third group is composed of compounds, many 
of which are insoluble in water, and are capable of being 
converted to some of the members of the second group. 
The members of the first group may all be converted to 
those of the second, but no method of changing the infe- 



2G6 THE FOURTH GROUP — TETRADS. 

rior sugars of the second class to the more valuable cane- 
sugar of the first has yet been discovered. 

313. Sucrose. — Sucrose (cane-sugar, C 12 H 22 O n ) is found 
in the juice of certain plants, as sugar-cane, sugar-maple, 
sugar-beet, sorghum, and many other plants. In the 
manufacture of cane-sugar from sugar-cane, the juice is 
pressed from the canes by passing them between rollers. 
The juice is treated with milk of lime and heated. The 
lime neutralizes the acids and the heat coagulates the 
albumen in the juice. The coagulated albumen rises and 
mechanically carries with it many of the impurities, some 
of which have combined with the lime. The scum thus 
formed is removed, and the liquid evaporated until it is 
of such a consistency that sugar crystals will form when 
the liquid is cooled. The crystals, when drained, are 
" brown " or " muscovado " sugar. The liquid remaining 
is molasses. 

(a) Brown sugar is refined by dissolving it in water, filtering the 
solution through layers of animal charcoal, and evaporating the water 
from the filtrate. When sucrose is boiled, part of it is changed to a 
mixture of dextrose and levulose, the proportion thus changed depend- 
ing upon the temperature and time of boiling. To lessen this loss of 
sucrose, the filtered solution is evaporated in large vacuum-pans from 
which the air and steam are exhausted. The degree of concentration 
desired is thus secured more quickly and at a lower temperature, les- 
sening the loss and obviating the risk of burning. When the " mother- 
liquor" drains from the crystals in molds, loaf-sugar is left; when 
it is driven off. by a centrifugal machine, granulated sugar is left. 

(/>) Formerly, sugar was made almost wholly from the sugar-cane 
and, as this grows only in a warm climate, nearly all of the sugar 
came from warm countries. More recently, large and increasing 
quantities of sugar are made from the sugar-beet. As this plant 
grows in a temperate climate, France, Austria, Russia, and the United 
States have become important sugar-producing countries. 'When in 



THE CARBOHYDRATES. 267 

the seventeenth century, sugar was first found to be a constituent of 
the beet, the beets contained only about 2 per cent of sugar. By 
skillful and long-continued cultivation, this percentage has been in- 
creased to 18 or 20. At the sugar factory, the beets are washed and 
cut into small, thiu strips. These strips are put into large iron vats 
with warm water which dissolves out some of the sugar. This first 
water is then replaced by a fresh supply, and the process repeated 
uutil all the sugar is extracted. This process of removing the sugar 
from the pulp is called the diffusion method, and is now largely used 
with sugar-cane also. The juice thus obtained is purified by lime, 
bleached by sulphurous oxide, and evaporated in vacuum-pans as in 
the other method of refining. 

(c) The sugar from the sap of the sugar-maple or from the juice 
of the sugar-beet is identical with cane-sugar. As the impurities of 
maple-sugar are agreeable to the taste of many persons, the sugar is not 
refined. Beet-sugar is always refined, as its impurities are offensive 
to all. 

((/) Sugar of milk or lactose (C 12 H 22 O u -f H 2 0) occurs in the milk 
of mammals. It is made from the whey of milk after the fat or 
butter, and the casein or cheese have been removed. It is less sweet 
and less easily soluble in water than cane-sugar. It may be used as 
a food by invalids and children who can not digest ordinary sugar. 
About 4 per cent of milk is lactose. 

(e) Maltose (C 12 H 22 O n ) is formed by diastase from starch in the 
process of brewing. 

00 When sugar is heated to about 210° or 220°, it loses water 
and is converted into caramel. 

314. Dextross and Levulose. — When a solution of 
sucrose is boiled with an acid or subjected to the action of 
yeast, it is converted into two isomeric varieties of sugar, 
dextrose (glucose, grape-sugar, starch-sugar, C 6 H 12 6 ), and 
levulose (fruit-sugar, C 6 H 12 6 ). 

Sucrose. Dextrose. Levulose. 

C 12 H 22 O n + H 2 = C 6 H 12 6 + C 6 H 12 6 . 

This mixture of dextrose and levulose is called invert- 
sugar. 



268 THE FOURTH GROUP — TETRADS. 

(«) Dextrose is found in many ripe fruits. The "candied" sugar 
of raisins and other dried fruits is dextrose. It crystallizes with diffi- 
culty and is generally found in a syrupy condition. It is prepared by 
boiling starch (C fi H I0 O 3 ) in water acidulated with sulphuric acid. It 
has less sweetening power than sucrose. Large quantities of glucose 
are now made from Indian corn. The corn-starch or potato-starch is 
boiled with dilute sulphuric acid for several hours. When it has 
cooled, the acid is neutralized with lime, and the solution is filtered. 
It is then evaporated to a syrup and sold as glucose or corn-syrup, or 
evaporated further to crystallisation, and sold as grape-sugar. Large 
quantities of both varieties are used in the manufacture of candies 
and syrups of all kinds and in the manufacture of alcoholic liquors. 
In the reaction, the acid does not enter into any combination, but 
facilitates the taking up of water by the starch. 
C 6 H 10 O 5 + 11,0 = C 6 II 12 6 . 

(b) Levulose is found w r ith dextrose in many ripe fruits, in honey, 
molasses, etc. It does not crystallize. It has less sweetening power 
than sucrose. 

(c) Dextrose and levulose may be fermented (Experiment 189) ; 
sucrose can not be fermented until after its conversion into dextrose 
and levulose. 

Starch. 

Experiment 212. — Grate a large potato on a fine grater, and stir the 
j)otato particles into about a quart of water. Allow the coarser par- 
ticles to settle, and decant the still white, milky liquid into another 
vessel. Let this stand for several hours, or until the liquid clears. 
Then pour off the water and dry the remaining starch. Boil a little 
of the dry starch in water. Largely dilute a little of the pa*te thus 
formed and test it with iodine as in Experiment 131. Successively 
dilute the remaining paste, testing a little of it after each dilution, 
and see how small a quantity of starch you can thus detect. 

Experiment 213. — Place a particle of the starch on a glass, add a 
drop of water, cover it with a thin cover-glass, and examine it with a 
microscope that magnifies about three hundred diameters. Observe 
the shape and markings of the granules. Make similar observations 
with corn-starch, wheat-flour, buckwheat-flour, tapioca, and sago. 
Compare the form and appearance of the several granules until you 
are able thus to identify the source of each. By sufficiently magnify- 
ing, the source of most kinds of starch may be positively identified. 



THE CARBOHYDRATES. 269 

315. Starch. — Starch (C 6 H 10 O 5 ) is a familiar substance 
found in grain (e.g., wheat and Indian corn), in the tuber 
of the potato plant and in the root, stem, or fruit of many 
other plants. It is composed of microscopic granules 
which, when heated in water nearly to the boiling-point, 
swell and burst, forming a pasty mass. This starch paste 
forms a blue color with iodine. 

(a) Tapioca, arrow-root, sago, and inulin are varieties of starch. 
The finest flour contains about 70 per cent of starch, and about 
10 per cent of gluten, a substance that in many respects resembles the 
white of eggs. 

316. Dextrin. — When a starch is heated to about 210°, 
it is changed to an isomeric compound called dextrin. 
Unlike starch, dextrin is soluble in cold water, forming a 
mucilaginous liquid. The adhesive compound on postage- 
stamps is largely dextrin. When starch is boiled in dilute 
sulphuric acid, it is converted first into dextrin and then 
into glucose. 

317. Bread -making. — In making bread, the water that 
is added to the flour forms a dough. The addition of 
yeast causes the starch to go to sugar, and fermentation 
to begin. As the fermentation proceeds, the carbon 
dioxide produced tends to escape through the tenacious 
dough, causing the latter to "rise." In the subsequent 
process of kneading, the half-fermented " sponge " is 
evenly distributed through the loaf and the large bubbles 
of gas imprisoned in the dough are broken up into smaller 
ones and the bread thus made finer grained. After 
kneading, the molded loaves are allowed to ferment again 
until they rise properly, when they are placed in a hot 



270 THE FOURTH GROUP — TETRADS. 

oven. The heat stops the fermentation, vaporizes the 
alcohol, and expands the vapor and the carbon dioxide. 
As these aeriform substances escape through the loaf, the 
loaf increases in size and "lightness." If the process has 
been satisfactorily conducted, by the time that the escape 
of gas and vapor has ceased, the walls of the bread cells 
will be strong enough to retain their form. If the dough 
is allowed to stand too long before baking, the gas will 
escape, the still plastic walls of the bread cells will collapse, 
and the bread " fall." If the oven is not hot enough or if 
the dough is too wet, a similar result will ensue and the 
bread will be " slack-baked." If the oven is too hot, a 
crust will form too quickly, the gas, being prevented from 
escaping, will collect at the center and the loaf be hollow. 
At the surface of the loaf, a substance much like caramel 
is formed ; this is the crust. The crust also contains 
dextrin. When the crust is moistened and the loaf 
returned to the oven, the dissolved dextrin left by evapo- 
ration gives to the crust a smooth, shining surface. 

The temperature at which the dough is kept during the 
fermentation is important. The yeast-plant grows best 
at a temperature of about 21° or 22°. If the sponge or 
dough becomes a few degrees cooler than this, the growth 
of the yeast is checked and the bread-rising stops. If 
the temperature is a few degrees higher, the growth of 
the germs of the acetic acid ferment is favored and that 
of the yeast-germs hindered, so that the dough becomes 
sour; then the bread will be sour and heavy. Success 
demands fresh, healthy yeast-plants to start the fermen- 
tation, and the maintenance of the temperature most 
favorable to their growth while the bread is rising. 



THE CARBOHYDKATES. 271 

Vegetable Parchment. 

Experiment 214. — Dilute 25 cu. cm. of sulphuric acid with 10 or 
12 cu. cm. of water. When the mixture is cold, immerse in it, for 15 
or 20 seconds, a piece of filter-paper. Rinse the paper in water and 
then in dilute ammonia-water, to remove all traces of the acid. 
Finally, rinse the paper again in pure water. The paper will have 
acquired greater toughness and rigidity and will resemble parchment 
in other respects. It has been changed to vegetable parchment or 
parchment-paper. It may be necessary to repeat the experiment, 
varying the time of immersion, to get good results. 

318. Cellulose. — Cellulose (C 6 H 10 O 5 ) constitutes the 
outer wall of every vegetable cell and is, therefore, found 
in every part of every plant. It may be said to form the 
framework of every vegetable tissue. It is insoluble in 
water or in alcohol, but* may be dissolved in concentrated 
sulphuric acid. By diluting and boiling this solution, 
the cellulose may be converted into dextrose and dextrin. 
Rags, paper, wood, and other forms of cellulose may thus 
be used in the preparation of glucose and alcohol. Linen 
and cotton are nearly pure cellulose. 

(a) Paper consists almost wholly of cellulose. The various forms 
of vegetable fiber used in its manufacture (linen and cotton rags, 
wood, straw, etc., according to the kind of product desired) are 
reduced to pulp partly by mechanical means and partly by boiling 
with caustic soda. This pulp diluted with the necessary amount of 
water is poured over an apron upon a steadily moving cloth made of 
fine brass wire specially woven for this purpose. The water drains 
from the pulp through this wire cloth. The paper gains in strength 
by the gradual loss of w T ater, until the web is strong enough to be led 
without breaking from the wire cloth to the press rolls, the drying- 
cylinders, etc. 

(b) By treating cellulose with a mixture of nitric and sulphuric 
acids, it is changed to gun-cotton (nitrocellulose, pyroxylin), an ex- 
plosive substance that burns in the air with a sudden flash and no 
smoke (see § 83). Gun-cotton may be considered to be cellulose with 



272 THE FOURTH GROUP — TETRADS. 

some of its hydrogen atoms replaced by the compound radical NO,. 
A solution of gun-cotton in a mixture of ether and alcohol, known as 
collodion solution, is much used in photography. Celluloid is an 
intimate mixture of gun-cotton and camphor. When heated, it is so 
plastic that it can easily be molded. It hardens as it cools. 

Albumin. 

Experiment 215. — Place a teaspoonful of the white of an egg in a 
test-tube ; add 25 cu. cm. of C 2 H 6 0. Xotice the coagulation. 

Experiment 216. — Place the remainder of the white of the egg in 
a test-tube ; place the test-tube and a thermometer in a vessel of 
water ; heat the water ; notice that at the temperature of about 60° 
the white of the egg coagulates. 

319. Albuminoids. — Albumin is composed of carbon, 
hydrogen, oxygen, nitrogen, and' sulphur — a very com- 
plicated structure. It is typical of a group of bodies 
(histogenetic) that are essential to the building up of the 
animal organism, of which group the leading members are 
albumin, fibrin, and casein. These differ but little, if 
any, in their chemical composition, but widely in their 
properties. They all exist in two conditions, — the soluble 
and the insoluble. 

(a) The white of the eggs of birds is the most familiar instance of 
albumin. It is soluble in water and coagulated by heat or alcohol. 
The albumin of plants is found chiefly in the seed. 

(b) Soluble fibrin is found in the blood. It hardens on exposure 
to the air and, entangling the corpuscles of the blood, forms the clot. 
By washing the clot with water, fibrin is left as a white, stringy mass. 
Insoluble fibrin constitutes muscular fiber. 

(c) Casein is found in the milk of animals. It is not coagulated 
by heat, but is coagulable by rennet, the inner membrane of the 
stomach of the calf. This property is utilized in cheese-making. 
Cheese contains from 10 to 40 per cent of fat and from 20 to 40 per 
cent of casein, most of the remainder being water. 



THE CARBOHYDRATES. 273 

(/I) All of the albuminoids are amorphous, and may be kept, when 
dry, for any length of time ; when moist, they rapidly putrefy and 
produce a sickening odor. 

Gelatin. 

Experiment 217. — Dilute a quantity of hydrochloric acid with 
about six times its volume of water. Place a clean bone (e.g., the 
femur of a chicken) in the dilute acid, and allow it to remain for 
three or four days. The mineral part of the bone will gradually 
dissolve, and there will be left a flexible substance that preserves 
the shape of the bone. 

Experiment 218. — Place the flexible substance left from the last 
experiment in water and boil it for three or four hours. It will dis- 
solve aud, when the liquid cools, will assume a jelly-like condition. 

320. Gelatin. — The bones and skins of animals contain 
a substance called ossein. The product of Experiment 217 
was ossein. When this substance is boiled in water, gela- 
tin is produced. The product of Experiment 218 was 
gelatin. Glue is an inferior quality of gelatin. 

321. Food of Animals. — The substances just considered, 
i.e., the sugars, starch, cellulose, albumin, and gelatin, con- 
stitute almost wholly the food of animals. The necessity 
for such food is threefold, — to build new tissue, to repair 
wasted or injured tissue, and to furnish heat. As almost 
all animal tissues are nitrogen-containing substances, the 
tissue-forming food-stuffs are of the albumin class (albu- 
minoids or proteids). The heat supply is chiefly met by 
the fats and the carbohydrates, starch and sugar (amy- 
loids). Only ruminant animals with special stomachs can 
digest cellulose freely. 

(a) Much the larger part of the needed food is required for heating 
purposes. Consequently, only a small proportion of the food necessary 
consists of meat and other nitrogenous foods except in the case of 

SCHOOL CHEMISTRY 18 



274 THE FOURTH GROUP — TETRADS. 

rapidly growing persons. Milk contains from 3 to 7 per cent of fat, 
about. 4 per cent each of sugar and casein, and 0.7 per cent of mineral 
matter. It is a well-proportioned food for growing persons, but is 
rather too high in nitrogenous constituents for persons whose tissues 
do not need heavy growth or repair. 

EXERCISES. 

1. Why does it require more sugar to sweeten fruits when the 
sugar is added before cooking than it does when the sugar is added 
after cooking? 

2. Write the formula for dextrin. 

3. Name the compounds symbolized as follows : BaO, I>a0 2 , 
Hg 2 0, HgO, N 2 0, NO, N 2 3 , N 2 5 , N0 2 . 

4. How many liters of chlorine are required for the combustion 
of 10 liters of defiant gas? C 2 H 4 + 2C1 2 = 4HC1 + C 2 . 

5. (a) Give a reaction for the preparation of carbon dioxide. 

(b) How may this gas be distinguished from every other gas? 

(c) How much of it is produced by burning 10 liters of marsh-gas? 

6. In the analysis of a certain compound, the following data were 
obtained : 

Carbon . . = 62.07 par cent. Oxygen . . = 27.58 per cent. 
Hydrogen . = 10.35 " " Vapor-density = 58 " " 

What is the molecular formula of the compound? What is the gen- 
eral formula of the acid series to which it belongs ? 

7. (a) Find the percentage composition of marsh-gas. (h) Of 
olefiant gas. 

8. What weight of KC10 3 is necessary to the preparation of 
35,000 cu. cm. of oxygen ? 

9. On completely decomposing, by heat, a certain weight of 
potassium chlorate, I obtained 20.246 grams of potassium chloride. 
(a) What weight of KC10 3 did I use? (b) What volume of oxygen 
did I obtain ? 

10. To inflate a certain balloon properly requires 132.74 kilograms 
of hydrogen. What weight of zinc will be needed to prepare this 
quantity of hydrogen? 

11. Explain the statement that in burning acetylene the heat given 
out by the combustion of its constituents is increased by the decom- 
position heat of the C2H2. 



OTHER ELEMENTS OF THE CARBON FAMILY. 275 

12. When a fat is heated with a stronger base than glycerin, the 
fatty acids leave the glycerin and combine with the metallic base. 
What is the name of the compound thus formed? 

13. State two ways in which albumin may be coagulated. 

14. Sketch in outline the several steps in the preparation of alcohol 
from cotton cloth. 

15. State in general terms the composition of carbohydrate mole- 
cules. 

16. In what way are alcohols and glycols analogous? 

17. How is carboxyl related to the basicity of a hydrocarbon acid ? 

18. What is the cause of the chemical changes involved in fer- 
mentation ? 

19. Of what is ordinary alcohol the hydroxide ? 

20. Of what hydrocarbon is chloroform a substitution product? 

VIII. OTHER ELEMENTS OF THE CARBON FAMILY. 

322. Rare Elements of this Family. — Titanium, zir- 
conium, cerium, and thorium are rare metals not found 
native. Their most common oxides are analogous to the 
dioxides of carbon and silicon. At 100° titanium decom- 
poses water, and at high temperatures it has the rare 
power of uniting directly with free nitrogen. When, 
as a metallic powder, titanium or cerium is sifted into 
a flame, it burns with dazzling brilliance. Zirconium 
dioxide is a white, infusible powder, and gives out an 
intense white light when heated. Like cerium dioxide, it 
forms a small constituent of the mantles used in gas- 
lighting by the Welsbach system. From ninety-eight to 
ninety-nine per cent of the Welsbach mantles consist of 
thorium oxide (Th0 2 ). A fine-meshed cotton cloth of 
the desired shape is saturated with nitrate of thorium and 
small proportions of the nitrates of zirconium and of 
cerium. When this is burned, the nitrates are decomposed 
and mantles of the oxides of the metals result. The com- 



276 THE FOURTH GROUP — TETRADS. 

bustion of the gas heats these mantles to such a degree of 

incandescence that they emit several times as much light 

as would the mere combustion of the same quantity of 

the s^as. -«-„-.•.„-- 

& EXERCISES. 

1. Describe the preparation and state the principal properties of 
H 2 S, HCN, CH 4 , and C 2 H 6 0. 

2. Write the symbols representing chloroform, glycerin, ether, 
acetic acid, cane-sugar, and starch. 

3. (a) Name the products of the combustion of common alcohol. 
(b) Describe briefly the process of preparing coal-gas, and tell its com- 
position. 

4. Name the substances symbolized as follows : KX0 2 , KX0 3 , 
KC1, KCIO, KC10 2 , KClOo, KC10 4 . 

5. (a) Find the weight of 20 liters of oxygen. (/>) Of 50 liters of 
chlorine, (c) Of 250 liters of NH 3 . 

6. What materials and what quantities would you need to prepare 
50 liters of each of the oxides of carbon ? 

7. By heating Mn0 2 with H 2 S0 4 the following reaction takes place : 

2Mn0 2 + 2H 2 S0 4 = 2MnS0 4 + 2H 2 + 2 . 
(«) What weight and (/>) what volume of oxygen can be thus obtained 
from 50 grams of manganese dioxide? 

8. (a) Give the ordinary methods of preparing oxygen, hydrogen, 
and hydrochloric acid, (b) In what do they differ, and in what do 
they agree? (c) Find the amount of chlorine, by weight and by 
measure, in 2 kilograms of hydrochloric acid. 

9. If 100 liters of C0 2 are required, by what means would you 
obtain it, from what materials, and what quantity of each material ? 

10. A taper is burned in a glass cylinder, at the bottom of which 
is a little lime-water. Explain the observed formation of a crust on 
the surface of the liquid. 

11. Show by a graphic formula that the compound radical car- 
boxyl (C0 2 H) is univalent. 

12. What is the molecular weight of ammonia gas? Determine 
from that weight the density of the gas. 

13. Increase threefold the number of each kind of atoms in a 
molecule of acetic acid. The molecular formula thus produced sym- 
bolizes two isomeric carbohydrates. Give the names of the tw r o sub- 
stances thus symbolized. 



THE SILICON FAMILY. 277 

IX. THE SILICON FAMILY. 

Silicox: symbol, Si; density (of crystals), 2.5; atomic weight, 28; 
valence, 4. • 

323. Silicon. — Although this element does not occur 
free in nature, it is the most abundant and widely diffused 
of the elements except oxygen. In combination as silica 
or as metallic silicates, it forms a large part of the earth's 
crust. 

(a) Free silicon may be prepared in several ways, but the pro- 
cesses are difficult and the element is rare. 

(b) Silicon exists, like carbon, in three allotropic forms; as a soft 
brown, amorphous powder that burns easily in air or oxygen forming 
Si0. 2 ; as hexagonal plates, corresponding to graphite in luster and 
electric conductivity; as needle-shaped octahedral crystals that are 
hard enough to scratch glass. 

(c) There is a compound of hydrogen and silicon known as hydro- 
gen silicide (SiH 4 ) that is somewhat analogous to CII 4 . Similar 
compounds are formed with members of the halogen group, as SiCl 4 , 
etc. 

324. Silicon Dioxide. — Silicon has only one oxide (silica, 
silicic anhydride, Si0 2 ). It is very abundant in 
nature. There are extensive mountain ranges 
that consist almost wholly of silicon dioxide. 
Its purest form is quartz or rock-crystal, which 
is found in beautiful hexagonal prisms ter- 
minated by hexagonal pyramids. Quartz has 
a density of 2.6, and is hard enough to scratch 
glass. 

(a) Amethyst, cairngorm stone, and rose-quartz are nearly pure 
crystallized silica. Agate, carnelian, chalcedony, flint, jasper, and 
onyx are nearly pure amorphous silica colored by traces of other 
oxides, as those of iron and manganese. White sand and sandstone 




278 THE FOURTH GROUP — TETRADS. 

are generally nearly pure silica. Siliceous sand and sandstone are 
often colored yellow by an iron oxide. 

(6) Silica is insoluble in water or in any acid except hydrofluoric. 

SiO, + 4HF = SiF 4 + 2H,0. 

The silicon fluoride thus formed is gaseous. Silica can also be slowly 
dissolved in a boiling solution of potassium or sodium hydroxide. It 
is dissolved in the waters of some thermal springs. The geysers of 
Iceland contain dissolved silica which is deposited by the cooling- 
waters upon objects immersed in them. Silica melts in the oxyhy- 
drogen flame to a colorless glass that remains transparent when cold. 

Silicic Acid. 

Experiment 2ig. — Place a few cubic centimeters of concentrated 
soluble glass in a small evaporating-dish and add strong hydrochloric 
acid until the mixture shows an acid reaction. A thick jelly-like 
mass will be formed in the liquid. Place the dish on a water-bath 
and evaporate its contents to dryness. Heat this solid residue gently 
over the lamp. It will diminish in volume. Add water and filter. 
The insoluble powder left upon the filter is precipitated SiO L „ one 
of the lightest known powders. The jelly-like mass formed in this 
experiment is principally silicic acid. 

Experiment 220. — Add some hydrochloric acid to a dilute solution 
of water-glass. Sodium chloride or potassium chloride will be formed 
with silicic acid. Pour the liquid mixture into a dialyser, made of 
parchment-paper stretched over a wooden ring and floated on the 
surface of pure water. The chloride solution passes through the 
membrane while the silicic acid remains dissolved in the dialyser. 
Crystallizable substances, like sodium and potassium chlorides, are 
sometimes called crystalloids, and uncrystallizable substances, colloids. 
Crystalloids and colloids may be separated as in this experiment. 
The process is called dialysis. 

325. Silicic Acid. — Normal silicic acid has the formula 
H 4 Si0 4 . It is so unstable that when it is set free from its 
salts, it at once breaks down to ordinary silicic acid, 
II 2 Si0 3 , the analogue of carbonic acid. 

H 4 SiG 4 = H 2 SiQ 3 + H 2 0. 



THE SILICON FAMILY. 279 

Most of the ordinary silicates are derivatives of this acid. 

Like carbonic acid, it is easily converted into the dioxide 

and water. 

H 2 Si0 3 + heat = Si0 2 + H 2 0. 

(a) By heating ordinary silicic acid, what are known as polysilicic 
acids may be formed. 

2H 2 SiQ 3 + heat = H 2 Si 2 O s + H 2 0. 
3H 2 Si0 3 + heat = H 4 Si 3 8 + H 2 0. 

Of these polysilicic acids, some of which are found in nature, opal is 
the best known example. 

326. Natural Silicates. — Silica unites with many me- 
tallic oxides to form silicates. The natural silicates are 
very numerous and many of them are of a very complex 
composition. Thus, clay is a silicate of aluminum ; feld- 
spar is a double silicate of aluminum and potassium ; 
mica is a triple silicate of aluminum, potassium, and iron. 
There are mountain ranges made up of these silicates. 

327. Artificial Silicates. — Sodium and potassium sili- 
cates (water-glass or soluble glass) are soluble in water ; 
they are largely used in the arts. The most important 
of the artificial silicates are glass and Portland cement. 
Glass is a mixture of a silicate of sodium or of potassium, 
or of both, with a silicate of one or more other metals. 
The composition is determined by the desired infusibility, 
insolubility, transparency, or color of the glass. 

(a) Bohemian glass is a silicate of potassium and calcium. It 
is fusible only with difficulty and is but little acted upon by chemi- 
cal reagents. It is free from color and is largely used in chemical 
apparatus. 



280 THE FOURTH GROUP — TETRADS. 

(b) Window-, crown, or plate glass is a silicate of sodium and cal- 
cium. It is harder than Bohemian glass, but more easily fusible and 
more readily acted upon by chemical reagents. 

(c) Bottle-glass, or common green glass, is a silicate of sodium, 
calcium, aluminum, and iron. Its color is due to the iron oxide pres- 
ent as an impurity in the cheap materials used. It is harder and 
more infusible than window-glass, but more easily acted upon by 
acids. 

(rf) Flint-glass is a silicate of potassium and lead. It has a high 
density and great refracting power. It is the most easily fusible 
variety of glass and is easily acted upon by chemical reagents. 
" Crystal " is a pure flint-glass used for optical purposes. " Strass " 
is a flint-glass very rich in lead and having a very high refractive 
power. It forms the basis of the artificial gems and precious stones 
known as "paste." 

(e) Glass softens at a red heat and can then be readily worked 
and welded (see Appendix, § 5). At higher temperatures it becomes 
still softer and finally melts. On cooling, it passes from a thin, mo- 
bile liquid through all degrees of viscosity to a hard solid. 

(/) Glass is acted upon readily by hydrofluoric acid (see Experi- 
ment 121). Etched glass is much used instead of the more expensive 
cut glass. 

(g) When glass, heated almost to redness, is dipped into oil heated 
to 300° and then allowed to cool gradually, it becomes toughened. 
Table glass thus toughened is not readily broken by falling or being 
thrown, but, when it is thrown with, sufficient force to break it. it is 
shattered into minute pieces. 

(h) Glass is easily colored by the addition of the proper materials 
to the fused mass. Thus, a green color is produced by the addition 
of a ferrous or cupric oxide ; blue, by a cobalt oxide ; violet, by man- 
ganese dioxide ; ruby, by gold, etc. 

(f) Portland cement is an artificial silicate made by strongly heat- 
ing together a very intimate mixture of nearly pure calcium carbon- 
ate, as limestone or marl, with a siliceous clay. The calcium unites 
chemically with the silica and alumina of the clay, producing silicates 
and aluminates of such a character that, when very finely ground and 
mixed with the proper proportion of water, they set to a solid stone 
more hard and durable than the best sandstone. It is a variety of 
"hydraulic" cement; i.e., it "sets" or hardens even under water. 
See § 180 (//). 



THE SILICON FAMILY. 281 

Note. — Carbon and silicon closely resemble each other in the 
composition of some of their simplest compounds. 



Carbon dioxide C0 2 

Carbonic acid .... H0CO3 

Marsh-gas CH 4 

Carbon tetrachloride . . . CC1 4 

Their points of difference are also well marked. 



Silicon dioxide .... SiO>2 

Silicic acid HoSi03 

Silicon hydride .... SiH 4 

Silicon tetrachloride . . SiCL 



328. Germanium. — The discovery of this element, 
which was made in 1886 by Winkler, was predicted in 
1871 by Mendeleef, from its place in the periodic system. 
It is a steel-colored metal with many properties analogous 
to those of tin. 

Tix: symbol, Sn ; density, 7.29; atomic weight, 118; valence, 2, 4. 

329. Source. — The principal tin ore is a dioxide called 
casserite or tinstone. It is found in but few localities, 
the principal ones being Cornwall in England, the island 
of Banca, and the Malay Peninsula. It has also been 
found in Australia, New Hampshire, Alabama, and Cali- 
fornia. Native tin has been found in small quantities. 

330. Preparation. — Tin is prepared by pulverizing, 
roasting, and washing the ore, and then smelting it with 
charcoal or anthracite. After the reduction is complete, 
the tin is drawn off and cast in bars. 

Properties of Tin. 

Experiment 221. — The familiar, so-called " tinware " is only tinned 
ware, iron coated with tin. Heat a piece of tinned iron over the lamp 
until the tin has melted ; thrust the plate into cold water to harden 
the tin quickly; remove the smooth surface of the metal by rubbing 
it first with a bit of paper moistened with dilute aqua regia, and then 
with paper wet with soda-lye. Notice the crystalline figures thus pro- 
duced, resembling frost upon a window pane. 



282 THE FOURTH GROUP — TETRADS. 

Experiment 222. — If you have a cake of tin, wash one surface of it 
with dilute aqua regia until the crystalline forms, above mentioned, 
appear. 

Experiment 223. — Hold a bar of tin near the ear and bend the bar. 
Notice the peculiar crackling sound. Continue the bending and 
notice that the bar becomes heated. The phenomena noticed seem to 
be caused by the friction of the crystalline particles. 

331. Properties. — Tin is a lustrous, soft, white metal, 
that melts at about 230°. It is highly malleable, slightly 
tenacious, ductile at 100°, and brittle at 200°. It has a 
marked tendency to crystallize on. cooling from a melted 
condition. It unites readily with ox}~gen, chlorine, sul- 
phur, and phosphorus when heated with them. It is not 
easily tarnished by even moist air but is easily acted upon 
by acids. Heated in the air, it burns to the dioxide. It 
forms two series of compounds, the stannous and the 
stannic. 

332. Uses. — Tin is largely employed in the form of 
foil, and as a coating for other metals; e.g., copper used 
for bath-tubs or cooking utensils, sheet-iron for "tin- 
plate " and iron tacks, and as a lining for lead water- 
pipes. It is largely used in making numerous alloys. 

(a) Bronze and bell-metal are alloys of copper and tin. Plumber's 
solder and pewter are alloys of lead and tin. Britannia metal is an 
alloy of copper, antimony, and tin. A common "silvering" of mirrors 
is an amalgam of mercury and tin. 

(7>) The tin of tinned ware is sometimes adulterated with lead, 
which is less costly. This alloy of lead and tin will oxidize much 
more readily than tin will. This lead oxide is easily dissolved by the 
C 2 H 4 2 of vinegar forming the dangerous poison, lead acetate or 
"sugar of lead." The various acids of our common fruits unite with 
the lead oxide to form salts, and all of the soluble lead salts are 
poisonous. 



THE SILICON FAMILY. 283 

333. Tin Compounds. — Tin forms two oxides, the mo- 
noxide (stannous oxide, S11O) and the dioxide (stannic 
oxide, Sn0 2 ). The former is basic; the latter is both a 
basic and an acid-forming oxide. Their compounds are 
designated as stannous and stannic salts. Stannic acid 
(H 2 Sn0 3 ) is a white solid. Stannous chloride (SnCl 2 ) 
is prepared by dissolving tin in warm hydrochloric acid. 
Tin tetrachloride (stannic chloride, SnCl 4 ) can be pre- 
pared by passing chlorine over tin-foil or over fused tin 
in a retort. If a quick stream of chlorine is forced 
through melted tin, heat and light are evolved. Stannic 
chloride is a colorless liquid which, when treated with 
one-third its weight of water, forms a crystalline mass 
called "butter of tin." When a solution of stannic 
chloride in water is boiled, stannic acid (H 2 Sn0 3 ) is 
formed as a precipitate. Although insoluble in water, 
this acid is easily soluble in hydrochloric, nitric, and 
sulphuric acids. When tin is treated with concentrated 
nitric acid, a white powder known as metastannic acid is 
formed. These two tin acids seem to have the same com- 
position, but as the latter is insoluble in acids as well as 
in water, the two can not be identical. 

Lead: symbol, Pb ; density, 11.37; atomic weight, 206; valence, 2, 4. 

334. Source of Lead. — Lead is seldom found free in 
nature, but its sulphide (galena, galenite, PbS) is quite 
abundant, and is, by far, its commonest ore. Galena is 
generally associated with silver sulphide. The United 
States produces more lead than any other country. 

335. Preparation. — The smelting of lead from its ores 
is carried out -in a reverberatory or in a blast-furnace. 



284 THE FOURTH GROUP — TETRADS. 

In the former case, the ore is first heated in an open 
furnace, in which part of the sulphide is oxidized, yield- 
ing lead oxide, sulphur dioxide, and lead sulphate. The 
furnace is then closed and heated to a higher temperature 
when the oxide and sulphate just formed act each upon 
a part of the still undecomposed ore, yielding metallic 
lead and sulphur dioxide. 

2PbS + 30 2 = 2PbO + 2S0 2 
PbS + 20 2 = PbS0 4 
PbS + 2PbO = 3Pb + S0 2 

PbS + PbS0 4 = 2Pb + 2S0 2 . 

In the blast-furnace process, lead ore, limestone, and 
some iron ore are mixed with coal and fused with an air- 
blast. The heat from the combustion of the coal melts 
the charge, while the lead sulphide burns to lead and 
sulphur dioxide, the silica and other impurities uniting 
with the calcium and iron to form a slag. 

The Lead Tree. 

Experiment 224. — To a solution of 5 grams of lead nitrate in a 
liter of water add two or three drops of nitric acid. Using this liquid 
instead of the solution of lead acetate, repeat Experiment 161. 

336. Properties. — Lead is a metal so soft as to be 
easily cut with a knife or indented with a finger-nail and 
to leave a streak when rubbed upon paper. It has con- 
siderable malleabilit}^ and little ductility. Repeated 
fusion renders it hard and brittle, probably by oxidation. 
When freshly cut, it has a bluish-gray color and a bright 
luster that is quickly dulled by oxidation. It melts at 
about 330°, and may be crystallized by slowly cooling a 



THE SILICON FAMILY. 285 

large quantity of the melted metal and pouring out the 
still liquid portion. It is very slightly acted upon by 
cold sulphuric or hydrochloric acid; its best solvent is 
nitric acid. It is precipitated in metallic form from a 
solution of one of its salts by metallic zinc. 

(a) Many potable waters and especially well-waters containing 
ammoniacal salts, often due to decaying organic matter, act upon 
lead with the formation of compounds that act as cumulative poisons. 
In many cases, the use of lead water-pipes is very dangerous for this 
reason. If, upon examining the inner surface of a lead pipe that has 
been thus used, it is found to be bright it may be known that danger- 
ous soluble salts have been formed and carried away with the water. 

(b) In the presence of air and moisture, lead is attacked by even 
feeble acids like acetic or carbonic acid. Hence, the use of cooking 
utensils that are made of lead or that contain lead even in the form 
of solder or as an adulteration of otherwise harmless substances some- 
times leads to the formation of poisonous lead compounds. When 
these are taken into the system, they unite with certain tissues of the 
body and are not readily eliminated. Thus the lead may accumulate 
until the quantity is sufficient to produce poisoning. For this reason, 
lead is called a cumulative poison. 

337. Uses. — Lead is largely used for many purposes on 
account of its softness, pliability, easy fusibility, and its 
comparative freedom from chemical action with water and 
most of the acids. 

338. Lead Oxides. — - Lead suboxide (Pb 2 0) is also called 
plumbous oxide. Lead monoxide (PbO) is also called 
plumbic oxide, but more frequently litharge. It is pre- 
pared on the large scale by highly heating melted lead in 
a current of air. It is used in the manufacture of glass. 
Red lead or minium (Pb 3 4 ) is largely used as a paint and 
in the manufacture of flint-glass. Lead dioxide (Pb0 2 ) 



286 THE FOURTH GROUP — TETRADS. 

or plumbic peroxide is most easily produced by treating 
red lead with -nitric acid. 

Pb 3 4 + 4HN0 3 = Pb0 2 + 2Pb(N0 3 ) 2 + 2H 2 0. 
The valence of lead in red lead is explained by the theory 
that red lead is a union of the dyad and the tetrad oxides. 

2PbO + Pb0 2 = Pb 3 4 . 

339. Lead Sulphide. — Lead sulphide (PbS) occurs na- 
tive as galenite or galena and may be prepared artificially 
by passing hydrogen sulphide into any solution of a lead 
salt, or by adding a soluble sulphide to such a solution. 
The precipitate thus formed is of a deep but varying 
color. This color, together with the insolubility of the 
precipitate, is of use in detecting the presence of lead. 

340. Soluble Lead Salts. —Lead nitrate [Pb(N0 8 ) 2 ] is 

readily formed by acting upon metallic lead with dilute 
nitric acid. Lead acetate [Pb(C 2 H 3 2 ) 2 ] is formed by 
dissolving litharge in acetic acid. It has a sweet, astrin- 
gent taste, whence its common name, " sugar of lead." 
The soluble lead salts are intensely poisonous. 

Insoluble Lead Salts. 

Experiment 225. — Add some hydrochloric acid to a dilute solution 
of lead nitrate or of lead acetate. A precipitate will be formed. Heat 
the liquid, and thus dissolve the precipitate. As the liquid cools, 
crystals of lead chloride will appear. 

341. Insoluble Lead Salts. — Lead chloride (PbCl 2 ), 
lead sulphate (PbS0 4 ), or lead chromate (PbCr0 4 ) is 
formed by adding a soluble chloride, sulphide, or chro- 
mate to a solution of a lead salt. Lead chloride is easily 
soluble in hot, but not in cold, water. Lead chromate is 



THE SILICON FAMILY. 287 

known as chrome yellow. Lead carbonate (PbC0 3 ) is 
formed as a white precipitate by adding ammonium car- 
bonate to a cold solution of lead acetate or nitrate. It 
occurs in nature as cerusite. White lead is a compound 
of varying proportions of lead carbonate and lead hydrox- 
ide. When ground with linseed-oil, it forms the basis of 
ordinary white paint, although zinc white is used for the 
same purpose. 

342. Lead Poisoning. — While metallic lead is not 
poisonous, all of its soluble salts are so in a very high 
degree. Lead acetate, given in doses of from three- 
tenths to six-tenths of a gram, produces symptoms of acute 
lead poisoning which often end fatally. Small doses of 
the oxides and carbonates frequently repeated often pro- 
duce chronic lead, poisoning. Painter's colic is a form of 
chronic poisoning by lead carbonate. Soluble sulphates, 
e.g., Epsom salt, are antidotes for lead poisons. 

343. Tests. — The sweet taste and poisonous character 
of the soluble lead salts render their detection a matter of 
great importance. 

(a) Any lead compound when heated on charcoal in the blowpipe- 
flame gives a bead of malleable lead. This bead is readily soluble in 
warm nitric acid; and this acid solution yields a precipitate with 
sulphuric acid. 

(7>) Potable waters suspected of containing lead compounds may he 
tested by slightly acidulating with hydrochloric acid and charging 
with hydrogen sulphide. If a black precipitate is formed, lead is 
probably present. The probability is sufficient to call for the services 
of a chemical expert. If lead salts are present in not too minute 
quantities, the addition of hydrochloric acid will yield a white cr} T s- 
talline precipitate of lead chloride which is soluble in an excess of 
boiling water. If the solution of the lead salt is tolerably strong, 
the addition of potassium iodide will generally yield a yellow pre- 



288 THE FOURTH GROUP — TETRADS. 

cipitate of lead iodide, while the addition of potassium chromate gives 
a fine yellow precipitate of lead chromate or chrome yellow. 

EXERCISES. 

1. (a) Write the reaction for the formation of lead oxide in the 
first stage of lead smelting, (b) For the formation of lead sulphate 
in the same stage. 

2. («) Express the reaction between the lead oxide and galenite 
in the second stage of lead smelting, (b) For the reaction between 
lead sulphate and the ore in the same stage. 

3. Why are lead compounds called cumulative poisons? 

4. Define normal, acid, basic, and double salts. Illustrate each. 

5. (a) What substance is represented by the formula 

O — Pb 

= Pb O? 

\ / 

O — Pb 

(b) What does this formula indicate concerning the valence of the 
lead atoms? 

6. What volume of C0 2 is produced by burning 1 liter of CII 4 ? 

7. What is the volume of 1 kilogram of oxygen ? 

8. Write the symbol for lead acetate. 

9. What is common washing-soda? Baking-soda? Why is the 
latter better for baking than the former? 

10. What name is given to a solution of calcium hydroxide in water? 

11. What is the percentage of carbon dioxide contained in calcium 
carbonate? 

12. Complete the following equation : Ca(OH) 2 + C0. 2 = 

13. A molecule of a certain oxide contains one atom of tin and 
has a weight of 150. What is its formula? 

14. How many liters of marsh-gas will weigh as much as 25 liters 
of ethene ? 

15. A certain compound has a molecular weight of GO. Its cen- 
tesimal composition is as follows : 40 of C, 53.4 of O, and 6.6 of H. 
What is the compound ? 

16. What weight of lead may be precipitated from a solution of lead 
acetate by 65 decigrams of zinc? (See Experiment 161. and §203.) 

17. What is the valence of tin in stannous compounds? In stannic 
compounds ? 



CHAPTER XV. 



THE FIFTH GROUP — PENTADS. 



344. The Nitrogen Family. — This family consists of ni- 
trogen, vanadium, columbium, praseodymium (see § 378), 
and tantalum. (See the table on page 145.) Nitrogen and 
its compounds have been considered in earlier chapters. 
The other members of this family are rare elements with 
properties that closely relate them to nitrogen. Some of 
these analogies are apparent in the formulas of some of 
their compounds : 



Xitrogen 


X.,0 


NO 


x,o, 


N0 2 


x,o 5 


HN0 3 


Gas 


Vanadium 


Y„0 


VO 


m 


V0 2 


V,O s 




Metal 


Colnnibiiim. 


— 


CbO 


— 


CbO, 


Cb 9 O s 


HCbOg 


Metal 


Praseodymium 


— 


— 


PrA 


Pr0 9 


Pr,O s 


— 


Metal 


Tantalum 


— 


— 


— 


Ta0 2 


Ta 2 5 


HTa0 3 


Metal 



Their symbols and atomic weights are given in the list of 
chemical elements printed in the Appendix. 

345. The Phosphorus Family. — This family consists of 
phosphorus, arsenic, antimony, and bismuth. Their char- 
acteristics show striking resemblances, as will soon appear. 
They are individually important. 

Phosphorus : symbol, P ; density, 1.8 ; atomic weight, 31 ; valence, 3, 5. 

346. Phosphorus. — This element does not occur free in 
nature, but its compounds with oxygen and some metal 

SCHOOL CHEMISTRY 19 289 



290 THE FIFTH GROUP — PENTADS. 

(chiefly calcium) are found in large quantities. Calcium 
phosphate is found as the native minerals apatite and 
phosphorite ; it forms, also, the greater part of the mineral 
constituent of animal bone. 

(a) The ultimate source of phosphorus is the granitic rocks, by the 
disintegration of which the fertile soil has been produced. All fruit- 
ful soils contain phosphates. These salts are diffused in such small 
quantities that their direct collection by the manufacturing chemist 
would be very costly. Plants collect the phosphates from the soil ; 
herbivorous animals obtain them by consuming the plants; from the 
bones of animals, the chemist derives the phosphates from which 
phosphorus is prepared. The process is devious and complicated, but 
the greater part of it is inexpensive. 

Note. — The name comes from two Greek words that mean -a 
bearer of light, phosphorus being luminous in the dark. The alche- 
mists used to call it " Son of Satan." Phosphides were formerly called 
phosphurets. 

Preparation of Phosphorus. 

See the Caution on page 15. Phosphorus burns are very difficult 
to heal. 

Experiment 226. — Mix intimately 25 grams of aluminum powder 
with 00 grams of sodium metaphosphate and 20 grama of powdered 
silica. Place the mixture in a good-sized combustion-tube (about a 
meter in length), the mouth of which is bent to dip beneath water. 



^P^fPirlffl - 



Fig. 75. MM 

Slowly heat the mixture to a moderate red heat, at the same time 
passing a slow current of hydrogen through the tube. Phosphorus 
will collect in the front part of the tube and may be expelled by heat 
into the water. 

6XaPO s -f 10A1 + 3Si0 2 = 3NaaSi0 3 + 5A1 2 3 + 6P. 



PHOSPHORUS. 291 

347. Preparation. — In the preparation of phosphorus, 
animal bones are burned and powdered. This powdered 
bone-ash is treated with sulphuric acid. This treatment 
yields an insoluble calcium sulphate (gypsum, CaS0 4 ) 
and a soluble salt, calcium acid phosphate, called " super- 
phosphate of lime." The insoluble sulphate is removed 
by filtration. The clear solution is then evaporated to a 
syrupy liquid, mixed with powdered charcoal, dried, 
heated, and finally distilled in earthen retorts, the necks 
of which dip under water. The liberated phosphorus 
condenses under the water. After purification, it is 
melted under hot water and run into cylindrical molds 
placed in cold water. 

(a) In the process just described, the following reactions take 
place. When the acid acts on the calcium phosphate of the bones : 

Ca 3 (P0 4 ) 2 + 2H 2 S0 4 = CaH 4 (P0 4 ) 2 + 2CaS0 4 . 

When the acid phosphate solution with charcoal is dried and heated, 
calcium metaphosphate is produced : 

CaH 4 (P0 4 ) 2 = Ca(P0 3 ) 2 + 2H 2 0. 

When the mixture is heated white-hot in the distillation retorts, cal- 
cium phosphate, carbon monoxide, and phosphorus are produced : 

3Ca(P0 3 )2 + IOC = Ca 3 (P0 4 ) 2 + 10CO + P 4 . 

(b) Large quantities of phosphorus are now T made by heating cal- 
cium phosphate w T ith carbon and silica to the intense heat of the 
electric furnace. The silica acts in the place' of the H 2 S0 4 of the 
older process, liberating phosphoric acid which is reduced by the car- 
bon : 

2Ca 3 (P0 4 ) 2 + IOC + 6Si0 2 = 6CaSi0 3 + 10CO + P 4 . 

Either mineral phosphates or the phosphates derived from bones may 
be used in this process. 

348. Physical Properties. — Pure phosphorus is an al- 
most colorless, translucent solid. The ordinary commer- 



292 THE FIFTH GROUP PENTADS. 

cial article has a feeble yellow tinge. When freshly cut, 
it has a garlic-like odor, often hidden by the odor of ozone 
which is generally present when moist phosphorus is 
exposed to the air. It is insoluble in water, sparingly 
soluble in turpentine, petroleum, and other oils, and easily 
soluble in carbon disulphide. It is soft and waxlike in 
warm weather but brittle at low temperatures. Under 
water, it melts at 44°, forming a viscid, oily liquid that 
boils at 290°, yielding a colorless vapor. At 500° the 
vapor is sixty-two times as heavy as hydrogen. Con- 
sequently, its molecular weight is 124, or four times its 
atomic weight. From this we conclude that the phos- 
phorus molecule contains four atoms and that each atom 
occupies half the space taken up by a hydrogen atom. 

Chemical Properties of Phosphorus. 

Experiment 227. — Bury a piece of phosphorus, the size of a grain 
of wheat, in a teaspoonful of lampblack or powdered bone-black that 
has been freshly prepared or recently heated. The oxygen con- 
densed within the pores of the carbon unites with the vapor of the 
phosphorus, developing enough heat to melt and finally to ignite 
the phosphorus. 

Experiment 228. — Dissolve a small piece of phosphorus in carbon 
disulphide. Pour some of the solution upon a piece of filter-paper 
placed upon the ring of a retort-stand. The volatile CS 2 soon evapo- 
rates, leaving the phosphorus in a finely divided state exposing a 
large surface to the oxidizing influence of the air. The phosphorus 
soon bursts into flame, which only partly consumes the paper. The 
burning phosphorus quickly covers the paper with a coat of incom- 
bustible and protecting varnish. If the experiment is performed in a 
dark room, the phosphorescence will be very marked. 

Experiment 229. — Rub a piece of dry phosphorus the size of a pin- 
head between two bits of board. The heat developed by the friction 
is sufficient to ignite it. Read the description of Experiment 6. 



PHOSPHORUS. 293 

Experiment 230. — Heat a small piece of phosphorus in a dry tube 
with a mere trace of iodine. Combination promptly takes place, a 
small quantity of volatile phosphoric iodide is formed and the rest of 
the phosphorus is changed to an allotropic form known as red phos- 
phorus. Try to repeat Experiment 229 with red phosphorus. 

Experiment 231. — Close one end of a piece of narrow glass tubing 
about 30 cm. long by fusing it in a flame. In the ignition-tube thus 
made place a small bit of red phosphorus and heat it gently in the 
lamp-flame. A yellow coating is quickly deposited upon the cool walls 
of the tube not far from the heated end. Allow the tube to cool, and 
cut off the end just below the yellow sublimate. Scratch this yellow 
deposit with a wire; it will take fire, as it is ordinary, yellow phos- 
phorus. By heating the red phosphorus, a part of it burned, thus 
removing the oxygen from the lower part of the tube. The inert 
nitrogen remaining there, enveloped and protected the rest of the 
phosphorus from combustion and thus permitted its reconversion into 
the ordinary variety. 

Experiment 232. — Touch a slice of phosphorus with a test-tube 
containing boiling water. The phosphorus will be ignited. 

Experiment 233. — Place a piece of phosphorus under water warm 
enough to melt it. Bring a current of oxygen from 
the gas-holder into contact with the melted phosphorus. 
The phosphorus will take fire and burn brilliantly under 
water. 

Experiment 234. — Upon a thin slice of phosphorus 
place a crystal of iodine. The two elements promptly 
unite with great energy, leading to the combustion of the 
excess of phosphorus. 

349. Chemical Properties. — Phosphorus combines read- 
ily with many of the elements, especially oxygen. It 
undergoes slow combustion at ordinary temperatures 
(forming P 2 3 ) and oxidizes with great energy at a 
temperature not much above its melting-point (forming 
P 2 5 ). On account of this easy inflammability, phos- 



294 THE FIFTH GROUP — PENTADS. 

phorus should be kept and cut under water and never 
handled with dry fingers. Owing to its slow combustion, 
it is feebly luminous in the dark. In distillation, the 
oxygen in the retort must be replaced by some inert gas 
like hydrogen, nitrogen, or carbon dioxide. Heated for 
several hours to about 240°, out of contact with oxygen 
or any other substance capable of entering into chemical 
union with it, it is changed to the remarkable allotropic 
modification known as red phosphorus. 

(«) The differences between the ordinary yellow and the red varie- 
ties of phosphorus are shown in the following table : 

Pale yellow Chocolate red. 

Strong odor Odorless. 

Density = 1.83 Density = 2.14. 

Phosphorescent Xot phosphorescent. 

Translucent Opaque. 

Soluble in carbon disnlphide . . Insoluble in carbon di sulphide. 

Subject to slow combustion . . Exempt from slow combustion. 

Melts at 41° Melts at 255°. 

Changes to red at 240° .... Changes to yellow at 300°. 

Soft Hard. 

Flexible Brittle. 

Poisonous Not poisonous. 

Chemically active Chemically inactive. 

350. Uses. — Phosphorus is extensively used in the 
manufacture of friction-matches, the match-tips generally 
being a mixture of phosphorus, glue, and potassium chlo- 
rate. Safety-matches are tipped with antimonious sulphide 
and potassium chlorate. These ignite, not by simple 
friction, but by rubbing on a prepared surface containing 
red phosphorus, manganese dioxide, and sand. Ordinary 
phosphorus mixed with flour paste is a rat poison that has 



PHOSPHORUS. 295 

probably led to the burning of many houses. Phosphorus 
is used in medicine ; many of the phosphates are impor- 
tant remedial agents. Phosphorus fumes produce, in the 
workmen in match factories, phosphorus-necrosis, a disease 
in which the bones of the jaw are destroyed. Taken 
internally, yellow phosphorus is extremely poisonous, a 
very small quantity causing death. There is no good 
antidote; the best treatment is promptly to give an 
emetic. 

EXERCISES. 

1. Symbolize two molecules of pentad phosphorus. 

2. (a) What is a binary molecule ? (&) A ternary molecule ? 
(c) How are binary molecules named? Illustrate. 

3. How much phosphorus is contained in 120 kilograms of bone- 
ash, of which 88.5 per cent is Ca 3 (P0 4 ) 3 and the rest is CaC0 3 ? 

4. (a) Find the percentage composition of carbon monoxide, 
(ft) Find the formula of a gas having the composition 27.27 per cent 
carbon; 72.73 per cent oxygen, and weighing 1.9712 grams to the liter. 

5. What elementary solid should never be handled with dry 
fingers? What one should never be handled with wet fingers? 

6. What is the meaning of the following : 

If from /ur)\Z^VfM C we ^ a ^ e ^ 2 0> ^\f\fM w ^ remain. 

7. What reason have we for thinking that phosphorus is tetra- 
tomic? 

8. How may the formula for acetic acid be derived from the 
formula for marsh-gas ? 

9. What are the products of the slow oxidation of alcohol? Of 
the quick oxidation ? 

10. Write the formula for potassium formate. 



Hydrogen Phosphide. 

Experiment 235. — Dissolve 20 grams of potassium hydroxide 
(caustic potash) in 50 cu. cm. of water. When the solution is cool, 



296 



THE FIFTH GROUP PENTADS. 



place it in a flask of not more than 100 cu. cm. capacity; add half a 
gram of phosphorus in thin slices, and 5 or 6 drops of ether; close the 

flask with a cork carrying a 
long glass delivery-tube that 
terminates beneath water. 
The ether is added that its 
heavy vapor may force the 
oxygen of the air from the 
flask ; when possible, it is bet- 
ter to use a current of illumi- 
nating-gas for this purpose. 
When the contents of the 
flask are boiled, gas escapes 
from the delivery-tube and 
bubbles up through the water. 
As each bubble of gas comes 




Fig. 77. 



into contact with the air, it bursts into flame with a bright light. If 
the air of the room is still, beautiful expanding rings of white smoke 
(P 2 5 ) will rise, with vortex motion, to the ceiling. At the end of the 
experiment, be careful that air is not sucked back into the phosphine 
in the flask. 

351. Hydrogen Phosphide. — This colorless, poisonous, 
ill-smelling gas (phosphureted hydrogen, phosphorus 
trihydride, phosphine, PH 3 ) is generally prepared by 
heating phosphorus in a strong alkaline solution. The 
reaction is complicated. 

(a) PH 3 is easily formed by placing calcium phosphide in water. 
Two other compounds of hydrogen and phosphorus are known of 
which one is liquid and the other solid at the ordinary temperature. 
Their proper formulas have not been definitely ascertained. 

(b) Pure PH 3 is not spontaneously combustible in the air. The 
combustion above noticed is due to the presence of a small quantity of 
the liquid phosphide just mentioned. If the gas, as it comes from the 
flask (Fig. 77), is passed through a tube chilled by a freezing mixture, 
this liquid (probably P 2 H 4 ) will be condensed. The escaping PH 3 
will not take fire as it subsequently bubbles through the water and 
comes into contact with the air. 



PHOSPHORUS OXIDES. 
(c) The composition of PH„ may be represented thus: 



297 



H 

1 



+ 



H 

1 



+ 



H 

1 



PH 5 
34 




In this case, the weight of half a unit volume is the atomic weight. 
The unit volume, being half the molecular volume, would include 
two phosphorus atoms. Compare the above diagram with the one 
given for ammonia. 

Phosphorus Oxide. 

Experiment 236. — Place a piece of thoroughly 
dry phosphorus weighing not more than a gram 
in a small, dry capsule ; place the capsule upon 
a large, dry plate ; ignite the phosphorus with 
a hot wire and quickly cover it with a dry bell- 
glass or wide-mouthed bottle of 2 or 3 liters' 
capacity. The capsule, plate, and bell-glass 
should be warmed to insure their being dry. 
A white, fleecy powder will be deposited within 
the bell-glass. Fig. 78. 

352. Phosphorus Oxides. — Phosphorus has two well- 
known oxides, the phosphorous and the phosphoric oxide. 

(a) Phosphorous oxide (phosphorus anhydride, phosphorus tri- 
oxide, P 2 O s ) is formed by the slow combustion of phosphorus in a 
limited current of dry air. It is a white, amorphous substance, very 
soluble in water and burns in the air to phosphoric oxide. It is said 
that its vapor-density indicates the formula P 4 (i . 

(6) Phosphoric oxide (phosphoric anhydride, phosphorus pentoxide, 
P 2 5 ) is formed by the combustion of phosphorus in an excess of 
oxygen. Its attraction for water is so great that it forms the most 
efficient known means of drying gases. If left in the air, it deliquesces 
completely in a few minutes ; if thrown into water, it hisses like a hot 
iron and dissolves with the evolution of much heat. It may be kept 
in dry tubes sealed by fusion. It is said that its vapor-density indi- 
cates the formula P 4 O 10 . 



298 THE FIFTH GROUP — PENTADS. 

353. Phosphorus Acids. — Phosphorus combines with 

oxygen and hydrogen to form a remarkable series of acids, 

as follows: 

H 3 P0 2 , bypophosphorous acid. 

P 2 3 + 3H 2 = 2ILP0 3 , phosphorous acid. 

< 3H 2 = 2H 3 P0 4 , phosphoric acid (ordinary or tribasic). 
P 2 5 4- J 2H 2 = H 4 P 2 7 , pyrophosphoric acid. 

I H 2 = 2HP0 3 , metaphosphoric acid. 

(a) HoP0 2 gives a series of salts known as hypophosphites ; e.g., 
sodium hypophosphite, XaH 2 P0 2 . When heated, it decomposes into 
H 3 P0 4 and PH 3 . It is monobasic. Its anhydride (P 2 0) has been 
claimed by some. 

(b) HgPOg may be formed by the action of water on P 2 3 , by the 
slow oxidation of phosphorus in moist air, or by the decomposition of 
phosphorus trichloride by water : PC1 3 + 3H 2 = H 3 P0 3 + 31IC1. 
When heated, it decomposes into H 3 P0 4 and H 3 P. Although it is 
dibasic, it is possible to displace its third atom of hydrogen to produce 
such compounds as sodium phosphite, Na 3 P0 3 , and triethyl phosphite 

(C 2 H 5 y ; ,Po 3 . 

(c) H,P0 4 may be prepared by the direct union of P 2 0- and boiling 
water, but the usual process is to oxidize phosphorus with nitric acid. 
When heated, it changes to II 4 P 2 O r or HP0 3 , as explained below. It 
is tribasic, and yields normal, double, and acid phosphates in great 
variety. It is sometimes called orthophosphoric acid. It and its 
salts are the most important of the phosphoric series. (See Exer- 
cise 3, p. 324.) 

(rl) H 4 P 2 7 is formed by heating H 3 P0 4 to 215°, thus depriving it 
of water : 

2H 3 P0 4 + heat = H 4 P 2 O r + H 2 0. 

It is tetrabasic and yields normal, double, and acid pyrophosphates in 
great variety. The group, PO (phosphoryl), acts as a trivalent com- 
pound radical. 



/OH 

(PO)^-OH 

M)H 



/OH 
— i 
OH 



(PO)^OH 
\ — 



f(PO)^oH 

>> t+H 2 0. 
| ( PO)/o„j 



PHOSPHORUS ACIDS. 299 

(e) HP0 8 is formed by the direct union of P 2 3 an( ^ co ^ wa ter, or 
by heating H 3 P0 4 to redness, thus depriving it of water : 

H 3 P0 4 = HP0 3 + H 2 0. 

It is monobasic and yields only normal metaphosphates. It is some- 
times called glacial phosphoric acid. It is said that its vapor-density 
indicates the formula H 2 P 2 () 6 . If its aqueous solution is boiled, it 
yields H 3 P0 4 . 

354. Tests. — With a solution of silver nitrate, a solu- 
ble phosphate gives a brown precipitate that is soluble in 
dilute nitric acid. With a nitric acid solution of molyb- 
dic acid containing ammonium nitrate, phosphates give 
bright yellow precipitates that are insoluble in dilute 
acids but soluble in ammonia. 

355. Plant Foods. — Plants derive all of their carbon 
from the air, but their mineral constituents and their 
nitrogen come from the soil. The chief mineral constitu- 
ents necessary for plant growth are silicon, calcium, mag- 
nesium, iron, sodium, potassium, and phosphorus. Silicon, 
calcium, iron, and sodium are present in most soils in 
quantities that can not be exhausted by plant growth. 
But by the continued cultivation of crops, the supply of 
available potassium, nitrogen, and phosphorus in the soil 
becomes exhausted unless the loss is made good. That 
they may become plant-food, these elements must be sup- 
plied in a form soluble in the plant juices so that they 
may be taken up by the plant roots. Most of the natural 
compounds of potassium and nitrogen are thus soluble, but 
the natural phosphates are insoluble and require chemical 
treatment to make them available as plant-food. 

356. Fertilizers. — The principal sources of phosphorus 
for fertilizers are rock phosphate [Ca 3 (P0 4 ) 2 ] and the 



300 THE FIFTH GROUP — PENTADS. 

bones of animals. These are insoluble in water or in 
plant juices. They are, therefore, ground and treated 
with sulphuric acid, forming calcium sulphate and calcium 
acid phosphate. 

Ca 3 (P0 4 ) 2 + 2H 2 S0 4 == 2CaS0 4 + CaH 4 (P0 4 ) 2 . 

This mixture is called by the trade name of " superphos- 
phate" and, with some salt of potassium and a nitrate (or 
an ammonia compound), constitutes the basis of most 
commercial fertilizers. 

EXERCISES. 

1. What is the valence of phosphorus in P2O5? Represent this 
molecule by its graphic formula. 

2. (a) What is the name of Ca // 3(P0 4 ) 2 ? (b) Why may not the 
f ornmla be written CaP04 ? 

3. Choose between HNa'P0 4 and msra 2 P0 4 . Give a reason for 
your choice. 

4. Write the empirical and the graphic formulas for the oxide of 
F". 

5. The formula for "microcosmic salt" is HNa(XH 4 )P0 4 . (a) 
What is the systematic name of the salt? (b) Is it a normal salt? 
Why? (c) Write the formula of the corresponding acid? (d) What 
is the basicity of that acid ? 

6. Symbolize disodium hydrogen phosphate, sodium dihydrogen 
phosphate, and normal sodium pyrophosphate. 

7. What is the systematic name of the sodium salt of monobasic 
phosphoric acid? 

8. If 2 liters of PH 3 are decomposed, what volume of phosphorus 
vapor will it yield ? 

9. Why is it that, while an atom of phosphorus is only 31 times as 
heavy as an atom of hydrogen, a liter of phosphorus vapor is 62 times 
as heavy as a liter of hydrogen? 

10. (a) Is Na' 3 P0 4 an acid salt? Why? (b) Is it a double salt? 
W T hy? (c) Is it a normal salt? Why? (7/) Is it a salt at all? 
Why? 

11. Can you write the formula for sodium hydrogen metaphosphate ? 



PHOSPHORUS. 301 

12. Give the empirical formula for the compound graphically 

symbolized as follows : 

(HO)\ 
(HO)/f-° 

O 

13. What does this last graphic formula intimate concerning the 
valence of the phosphorus? 

14. If one atom of oxygen in a molecule of metaphosphoric acid is 
replaced by two of hydrogen, what will result ? 

15. What is represented by O = P = ? 

16. Write the reaction for the combustion of one molecule of 
phosphorus in an excess of oxygen. 

17. Ca" 3 P 2 + 6HC1 = 3CaCl 2 + 2 . Complete the equation. 

18. Write the reaction for the decomposition of H3PO2 by heat. 

19. What is the difference between a phosphide and a phos- 
phuret ? 

20. (a) What is the valence of phosphorus in H3PO3? (ft) In 
H 3 P0 4 ? 

21. The tube represented in Fig. 79 has a fine opening at a, burn- 
ing phosphorus at c, and a 
tube, e, connected with an ^ 

aspirator so that a current 

Fig 79 
of air maybe drawn through 

the apparatus. What is the product of the combustion? 

22. I have a substance insoluble in carbon disulphide; it causes 
HNO3 to give off red fumes, and forms with it H3PO4. What is the 
substance? What are the red fumes? 

23. (a) If from the imaginary double molecule, 2H5PO5, we take 
2H 2 0, what will remain? (b) What, if we take 3H 2 0? (c) What, 
if we take 4H 2 ? (d) What, if we take 5H 2 ? 

24. (a) If in a molecule of tribasic phosphoric acid one of the 
univalent hydroxyl groups is replaced by an atom of hydrogen, what 
will result? (b) What, if two such groups are replaced by H 2 ? 

25. If a liter of PH 3 is decomposed by the passage of a series of 
electric sparks, what volume of hydrogen will it yield? 

26. Write the formulas for phosphorus trihydrate and phosphoryl 
trihydrate. 



302 THE FIFTH GROUP — PENTADS. 

27. Give the name of the compound graphically symbolized as 

follows : 

(HO)— P— O— (HO) 

O 

I 
(HO)— P— O— (HO) 

28. What does the above graphic formula intimate concerning the 
valence of the phosphorus? 

Arsenic : symbol, As ; density, 5.6 to 5.9; atomic weight, 75 ; 
valence, 3, 5. 

357. Arsenic. — Arsenic is widely distributed in small 
quantities. It is sometimes found free in nature but more 
frequently combined with iron, sulphur, and other ele- 
ments. It is generally prepared from arsenical pyrite 
(mispickel, FeAsS) by sublimation, or from its oxide by 
reduction with charcoal. 

358. Properties and Uses. — Arsenic has a metallic luster 
and a steel-gray color. Its vapor is 150 times as heavy as 
hydrogen. In its physical properties, it closely resembles 
a metal; in its chemical properties, it more closely resem- 
bles a non-metal. It has been called "the connecting 
link" between the metallic and the non-metallic elements, 
being closely connected with antimony and bismuth on the 
one hand, and with phosphorus and nitrogen on the other. 
Like phosphorus, its molecule contains four atoms, as is 
shown by its vapor-density (§ 136, a). Most of its solu- 
ble compounds are active poisons. Heated in the air, it 
burns, forming the trioxide. It is used in the manufacture 
of shot and of fireworks. 

Note. — The "arsenic" or "white arsenic"of the druggist is arsenic 
trioxide (AS2O3). The arsenides were formerly called arseniurets. 



ARSENIC. 303 

359. Hydrogen Arsenide. — This very poisonous gas 
(arsine, arseniureted hydrogen, AsH 3 ) may be formed by 
the action of dilute sulphuric acid upon zinc and any 
arsenic-containing compound, because all arsenical com- 
pounds are reduced to the hydride by nascent hydrogen. 
In its preparation, great care must be taken not to breathe 
any of the gas or to allow it to escape into the room, as it 
is extremely poisonous. Very small quantities have been 
known to produce death. When burned in the air, it 
yields water and arsenic trioxide. When heated without 
access of air, it is dissociated into arsenic and hydrogen. 
Its volumetric composition is similar to that of hydrogen 
phosphide. 

(«) XH 3 has strong basic properties; PH 3 has weak basic proper- 
ties ; AsH 3 has no basic properties. 

Arsenic Trioxide. 

Experiment 237. — Place a small quantity of arsenic trioxide in a 
tube of hard glass about 10 cm. long, and hold the tube in a sloping 
position in a lamp-flame until the powder is volatilized. With a 
magnifying lens, examine the walls of the tube where the trioxide 
has condensed ; the oxide will be seen to be crystalline. 

Experiment 238. — Make the tube used in the last experiment into 
an ignition-tube by fusing and sealing one end of it in the lamp- 
flame. In the bottom of the tube thus formed, place a little (a few 



milligrams only) of arsenic trioxide and above it a small piece of 
charcoal, as shown- at c. Holding the tube horizontal, heat the char- 
coal splinter to redness; then gradually bring the tube into a nearly 
vertical position, keeping the charcoal red-hot and heating the tip of 



304 THE FIFTH GROUP — PENTADS. 

the tube until the trioxide is vaporized. The vapor will be reduced 
by the glowing charcoal and a brilliant ring of metallic arsenic will 
appear at a. 

360. Arsenic Oxides and Sulphides. — Arsenic trioxide 
(arsenious oxide, arsenious anhydride, white arsenic, 
As 2 3 ) is prepared on the large scale by roasting arsenical 
ores with free access of air. The arsenic thus oxidized 
and volatilized appears as white fumes that are led into 
large chambers where they are condensed to a white pow- 
der. Arsenic trioxide occurs in three varieties, the amor- 
phous or vitreous, and two different crystalline fornix, 
rhombic and octahedral. It is feebly soluble in water, 
but dissolves more readily in boiling hydrochloric acid, 
and freely in alkaline solutions. Heated in contact with 
air, it volatilizes without change. Heated in contact with 
carbon, it gives up its oxygen and is reduced to metallic 
arsenic. As a poison it is very dangerous, because it has 
no warning odor and scarcely any taste, and because very 
small quantities produce death. Its best antidote is 
freshly prepared ferric hydroxide which forms with it an 
insoluble salt and thus prevents the poison from entering 
the system. When these can not be quickly obtained, an 
emetic should be promptly administered. Arsenic triox- 
ide is largely used in the manufacture of pigments and of 
glass, as a mordant in cotton printing, and as an insecti- 
cide. As the vapor-densit}' of this substance is 198, its 
molecular formula is sometimes written with apparent 
propriety, As 4 6 . 

(a) Arsenic pentoxide (arsenic anhydride, As 2 Or,) maybe obtained 
by oxidizing the trioxide with nitric acid, evaporating to dryness, and 
heating nearly to redness. It is less powerfully poisonous than the 
trioxide. 



ARSENIC ACIDS. 



305 



(b) Two native sulphides of arsenic are found. The red sulphide 
(AS2S2) is called realgar ; it is used in making fireworks. The yellow 
sulphide (AS2S3) is called orpiment; it is used as a pigment. In addi- 
tion to the disulphide and the trisulphide, a pentasulphide (AS2S5) is 
obtained by fusing the trisulphide with sulphur. 

361. Arsenic Acids. — Arsenic forms a series of acids 
that presents remarkable analogies to the phosphorus 
acid series. 

AsoOs + 3HoO = 2H 3 As0 3 , arsenious acid. 

f 3H 2 = 2H 3 As0 4 , tribasic arsenic acid. 

As20 5 + •! 2H2O = H 4 As 2 P pyroarsenic acid. 
I H 2 = 2HAs0 3 , nietaarsenic acid. 

(«) When AS.2O3 is dissolved in water, the solution gives a feebly 
acid reaction and is supposed to contain H3ASO3. The corresponding 
salts are called arsenates ; e.g., silver arsenite, Ag3As03. 

(h) H 3 As0 4 is generally prepared by treating AS2O3 with nitric 
acid. The commercial form is a liquid, from which transparent 
crystals may be obtained by cooling. As it is tribasic, it yields three 
series of arsenates which closely resemble the corresponding phos- 
phates in composition and crystalline form. Heated to 180° it loses 
water and becomes H 4 As 2 7 . Heated to 200° it loses another mole- 
cule of water and becomes HAsOs- 

Marsh's Test for Arsenic. 

Experiment 239. — Arrange the ap- 
paratus for the preparation of dry 
hydrogen, using a cold mixture of 1 
part of sulphuric acid and 3 parts of 
water. It is well to keep the gener- 
ating flask cool by placing it in a cold 
water-bath. When the air has been 
expelled from the apparatus, ignite 
the jet. Hold a piece of cold porce- 
lain in the flame, and notice that no 
colored stain is produced. (If a stain 
should appear, it would show that 
the materials used in the generating 
flask were impure.) Keep the jet 

SCHOOL CHEMISTRY 20 




Fig. 81. 



306 THE FIFTH GROUP — PENTADS. 

burning and add, through the funnel-tube, a few drops of a hot aqueous 
solution of AS2O3. Notice the change in the appearance of the flame. 
Hold the cold porcelain in the flame. A stain having a metallic 
luster will be produced. The stain is metallic arsenic, freed from 
combination in ASH3 by the heat of the flame and deposited, just as 
soot would be by a candle-flame. Do not let the porcelain become 
hot enough to vaporize the arsenic and to cause the stain to disappear. 
Keep the jet burning until the apparatus is placed in the ventilating 
closet or out of doors, to prevent the escape of AsHs into the room. 

Experiment 240. — Clean the generating flask and repeat the experi- 
ment, using " Paris green " instead of the AS2O3. 

Experiment 241. — Boil a green-paper label with hydrochloric acid 
in a test-tube. Test this solution for the presence of arsenic, as in 
Experiment 239. Try the same with green wall-paper or with green 
paint scraped from woodwork. 

Note. — Formerly, cloth and paper were often colored green by 
arsenic-containing coloring matters. These dangerously poisonous 
substances have now been largely (but not wholly) replaced by coal- 
tar dyes free from arsenic. Arsenical green paints are still common. 

Experiment 242. — After passing the Asli 3 through a drying-tube 
containing potassium hydroxide and calcium chloride, as shown in 
Fig. 81, heat the delivery-tube to a red heat. The gas will be de- 
composed, the arsenic being deposited as a dark band ("mirror of 
arsenic ") upon the cool part of the tube and the hydrogen burning 
with its characteristic flame at the jet. Little or no deposit will then 
be made on the cold porcelain. 

Experiment 243. — To show that the stains produced in Experi- 
ments 239 and 240 are arsenic and not antimony, which might imitate 
them, touch one of the stains with a glass rod dipped into a solution 
of chloride of lime. If the metal dissolves, it is arsenic. 

362. Marsh's Test. — The preceding experiments rudely 
illustrate Marsh's test for arsenic. The test is so deli- 
cate that a hundredth of a milligram (yoVo °f a grain) 
of the poison may be recognized with certainty. In ex- 
aminations of great importance, as in trials for murder 



ARSENIC. 307 

by arsenical poisoning, the purity of all materials used 
and the nature of the metallic deposit are carefully de- 
termined by confirmatory tests. 

EXERCISES. 

1. Writs the equation representing the combustion of hydrogen 
arsenide. ■ 

2. What is the weight of 10 As 2 3 ? 

r 3. Name the following: H 3 As6 4 ; XaH 2 As0 4 ; Xa 2 HAs0 4 ; 
Na 3 As0 4 . 

4. Write a graphic formula for H 3 P'"0 3 . 

5. When AsH 3 is prepared from Zn 3 As 2 and dilute sulphuric 
acid, zinc sulphate is produced. How much AsH 3 , by weight and by- 
volume, can be prepared from 50 grams of Zn 3 As 2 ? 

6. Why is As 2 3 said to be dimorphous ? 

7. What is a dyad? A monobasic acid? 

8. You are given a mixture of ordinary and red phosphorus. 
How will you separate the two varieties? 

9. Name two elements that are thought to be tetratomic, and give 
a reason for such belief. 

10. What volume of steam will result from the burning of 100 
grams of hydrogen ? 

11. Write the formula for sodium acetate. Remember that sodium 
is a monad. 

12. Write the formula for copper acetate. Copper is a dyad. 

13. Write the reaction for Experiment 238. 

14. Write the reaction for the preparation of arsenic from arsenical 
pyrite. 

15. Is tartaric acid monobasic? If so, why? If not, why not? 

16. Rochelle salt is sodium-potassium tartrate with four equivalents 
of water of crystallization. Write the formula for Rochelle salt. 

Antimony : symbol, Sb ; density, 6.7 ; atomic weight, 119 ; valence, 3, 5. 

363. Antimony. — The antimony of commerce is ob- 
tained from the mineral stibnite, which is an antimony 
trisulphide (gray antimony, antimony glance, Sb 2 S 3 ). 
Antimony is, however, found native and in combination 



308 THE FIFTH GROUP — PENTADS. 

with other elements than sulphur. The stibtiite is first 
melted to remove earthy impurities, and is then fused 
with about half its weight of iron (Sb 2 S 3 + Fe 3 =3FeS + 
Sb 2 ), or roasted in a reverberatory furnace and reduced 
with coal. It may also be prepared by the electrolysis of 
its salts. 

Properties of Antimony. 

Experiment 244. — With the blowpipe heat a small piece of metallic 
antimony on charcoal. Similarly heat a small piece of arsenic. No- 
tice the effect in each case, and see if in this way you can distinguish 
between arsenic and antimony. 

Experiment 245. — Repeat Experiment 239, using a solution of 
tartar emetic instead of the solution of arsenic trioxide. Note in 
what respects the antimony spot differs from the arsenic spot. 

Experiment 246. — Make two molds by boring conical cavities in 
a block of plaster of Paris. See that each mold terminates below in a 
sharp point. Make two or three clean-cut grooves in the sides of the 
molds. Into one mold, pour melted lead ; into the other, melted type- 
metal. Remove the casts, and notice that the lead cone is blunted at 
the apex while the type-metal is pointed; that the ridges on the sides 
of the lead cone are ill defined, while those on the sides of the type- 
metal are well defined. The lead contracts as it cools and thus shrinks 
from the mold. The type-metal is composed of about 70 parts of lead, 
10 parts of tin, and 20 parts of antimony. The tin gives it tough- 
ness, and the antimony hardness. The antimony tends to crystallize 
as it cools, thus causing the type-metal to expand, to force itself into 
every part of the mold, and to make a sharply defined cast. 

364. Prop3rties and Uses. —Antimony is a bluish-white 
metal. It is so brittle that it may be powdered in a 
mortar. Its crystalline tendency is so strong that, when 
it is cooling from the melted condition, beautiful fernlike 
figures are formed on the free surface of the metal. These 
figures may be seen on one surface of almost every cake 
of antimony found in commerce. Antimony melts at 



ANTIMONY. 309 

450°. It is not acted upon by the air at ordinary tem- 
peratures, but when melted in contact with the air it 
rapidly oxidizes. At a red heat, it burns with a white 
flame, forming antimony trioxide (Sb 2 3 ). It is a con- 
stituent of tartar emetic, and is largely used in the arts 
as a constituent of type-metal, britannia and bearing 
metals, pewter, and other valuable alloys. 

(«) Antimony is strongly attacked by chlorine (Experiment 90), 
forming SbCl 3 . It is not acted upon by dilute hydrochloric or sul- 
phuric acid, but it is easily dissolved by aqua regia. Xitric acid 
acts upon it, forming insoluble Sb 2 O s . 

(b) Antimony is an acid-forming and a base-forming element, as 
are nitrogen and phosphorus. Some of its basic compounds in neu- 
tralizing acids form salts in which the basic hydrogen of the acids is 
replaced by antimony. Xeither nitrogen nor phosphorus can thus 
replace the hydrogen of an acid. 

365. Antimony Compounds. — The compounds of anti- 
mony correspond closely to those of arsenic. 

(a) Hydrogen antimonide (stibine, antimoniureted hydrogen, 
SbH 3 ) is formed when a soluble compound of antimony is acted upon 
by nascent hydrogen. It is analogous to arsine, but its metallic de- 
posit is easily distinguished from that of the latter compound by its 
darker color, smoky appearance, non-volatility, and other tests. Its 
combustion yields H 2 and Sb 2 3 . 

(6) There are three known oxides of antimony, represented by the 
formulas Sb 2 3 , Sb 2 4 . and Sb 2 5 . The tetroxide may be considered 
a mixture of the other two : Sb.,0 3 + Sb 9 0- = 2Sb O 4 . These oxides 
form acids that resemble the phosphorus acids. There are also two 
sulphides (Sb 2 S 3 and Sb 2 S 5 ) and two chlorides (SbCl 3 and SbCl 5 ). 
The trichloride is a soft solid, known as butter of antimony; the 
pentachloride is a strongly fuming liquid. 

Bismuth: symbol, Bi; density, 9.8; atomic weight, 207; valence, 3, 5. 

366. Bismuth. — Bismuth is found in nature free, and 
in combination with oxygen (Bi 2 3 ), or with sulphur 



310 THE FIFTH GROUP — PENTADS. 

(Bi 2 S 3 ). In its preparation, bismuth ores are roasted and 
then smelted in a pot with iron, carbon, and slag. The 
crude bismuth is drawn off in a melted condition from 
the bottom of the smelting pot after the layer of less 
easily fusible "cobalt-speiss" above has solidified. Most 
of the bismuth of commerce comes from Saxony and 
Bohemia. 

Crystallization of Bismuth. 

Experiment 247. — Melt 2 or 3 kilograms of bismuth in a crucible. 
Perforate the covering crust that forms on cooling and pour out the 
still molten liquid within. "When cool, break the crucible to obtain 
a view of the beautiful bismuth crystals thus formed. 

367. Properties and Uses. — Bismuth is a brittle, bril- 
liant, pinkish-white metal that, except in color, looks like 
antimony. Of all known substances, it is the most dia- 
magnetic. In cooling from fusion, it crystallizes more 
readily than any other metal. Its crystals are nearly 
cubical rhombohedrons, often beautifully iridescent from 
the film of oxide formed when the crystals were still hot. 
It melts at 264° and expands in solidifying. In dry air 
at ordinary temperatures it is unaltered, but, when 
strongly heated, it burns with a bluish-white flame form- 
ing yellow bismuth trioxide (Bi 2 3 ). It is used in form- 
ing alloys and in the construction of thermoelectric piles. 

(a) Bismuth is acted upon readily by chlorine. Cold hydrochloric 
and sulphuric acids have no action upon it. Its best solvents are 
nitric acid and aqua regia. It has four oxides, viz., Bi.,().„ Bi.,0.,, 
Bi 2 4 , BigOg. When the metal is dissolved in nitric acid and the 
solution is evaporated to dryness, bismuth nitrate [Bi(NO a )J is 
obtained. Such salts, in which bismuth acts as a trivalent metal, are 
called bismuth salts. In another class of compounds, called bismuthyl 
salts, the group BiO (bismuthyl) acts as an univalent compound 



BISMUTH. 



311 



radical, as in bismuth yl nitrate. When bismuth nitrate is decom- 
posed by heat or by -water, basic nitrates or "subnit rates" of bismuth 
are formed. These are of varying composition, but all of them are 
the products of the incomplete neutralization of the basic compound, 
Bi(OH) g . 

Fusible Alloys. 

Experiment 248. — Place 30 grams of bismuth, 15 grams of lead, 
and 15 grams of tin in boiling water. Let the metals remain there 
until you are convinced that none of them can be thus melted. Then 
place them in an iron spoon, melt them together and pour the molten 
mass into cold -water. Immerse the alloy thus formed in boiling 
water and notice that it melts. Pour the liquid alloy into a small 
test-tube and allow it to cool. Notice that, after several minutes, the 
cooling and expanding metal bursts the glass walls that confine it. 

368. Fusible Metals. — Bismuth forms, with certain 
other metals, alloys that melt at a temperature far below 
the melting-point of any of their constituents. The com- 
position and melting-points of some of these are given in 
the following table : 





Nbwtow's 

Metal. 


Eose's Metal. 


Lichtexbeeg's 
Metal. 


Wood's Metal. 


Bismuth . . . 
Lead .... 
Tin .... 
Cadmium . . 


8 parts 
5 " 
3 " 
" 


2 

1 
1 



5 
3 
9 




4 
2 

1 
1 


Melting-point . 


91.5° 


93.75° 


91.6° 60.5° 



These melting-points may be still further reduced by 
the addition of mercury. It will be noticed that any of 
these fusible metals will melt in boiling water. If any 
of them is melted and poured into a glass vessel, the 
expansion will burst the glass when the metal cools. 



312 THE FIFTH GROUP — PENTADS. 

These alloys are used in obtaining casts of woodcuts, etc., 
the cast being made when the metal has so far cooled as 
to be viscid. Lead, tin, and bismuth are mixed in such 
proportions that the alloy melts at some particular tem- 
perature above 100° for the making of safety-plugs for 
steam-boilers. As soon as the steam reaches the pressure 
corresponding to the melting-point of the alloy, the plug 
melts and the steam escapes. These alloys are also used 
in the automatic sprinkling devices for extinguishing fires 
in buildings. The rooms to be protected are supplied 
with pipes and sprinkling devices containing water under 
pressure. These pipes are closed with a fusible metal 
alloy. When a fire occurs, the heat melts the easily 
fusible alloy causing the room to be flooded with water 
from the sprinklers. 

369. The Pentad Group. — The members of this group, 
and especially the members of each family of this group, 
have certain well-marked resemblances. Thus the hydrides 
of nitrogen and of phosphorus have strong analogies that 
override family lines, while the resemblances of the oxides 
and the acids of nitrogen and of phosphorus are far from 
complete. But between phosphorus, arsenic, and antimony. 
and between antimony and bismuth, the resemblances are 
very close. There is an increase in density, atomic weight, 
and metallic characteristics from nitrogen to bismuth, and 
(in a general way) an increase in chemical activity from 
bismuth to nitrogen. In the phosphorus family, each of 
the elements crystallizes in two forms ; i.e., each is dimor- 
phous. In the case of each of the four members of this 
family, these two crystal forms are the same; i.e., these 



THE PENTAD GROUP. 313 

four elements are isomorphous. The atomic weight of 
arsenic differs but little from the arithmetical mean of 
the atomic weights of phosphorus and antimony, and the 
atomic weight of antimony bears a similar relation to the 
atomic weights of phosphorus and bismuth. These rela- 
tions have a significance confirmatory of the theory that 
the properties of the chemical elements are really periodic 
functions of their atomic weights (see § 148). 

EXERCISES. 

1. Write the reaction for Experiment 90. 

2. What is meant by the statement that As 2 3 and Sb.,0 3 are 
isodimorphous ? 

3. When a current of hydrogen disulphide is passed through a 
solution of SbCl 3 , Sb 2 S 3 and an acid are formed. Write the reaction. 

4. Write a graphic formula for tribasic phosphoric acid, represent- 
ing it as a compound of pentad phosphorus. 

5. Write a graphic formula for hypophosphorous acid representing 
it as a compound of trivalent phosphorus. 

6. (a) How is P 2 5 made? (Ij) How many distinct phosphoric 
acids can be formed? Give their names and formulas. 

7. Write the formula for bismuthyl nitrate. 

8. When iodine and red phosphorus act upon each other in the 
presence of water, the reaction rnay be represented thus : 

•P + 51 + 4H 2 = 5HI + H 3 P0 3 . 

What weight and what volume of the binary acid gas can be 
obtained by using 10 grams of phosphorus? 

9. Write the structural formula for bismuth hydroxide. 

10. Write the formula for antimoniureted hydrogen. How does 
it differ from that of stibine ? 

11. What is a chemical compound? How do you find the combin- 
ing weights of compounds? Illustrate by potassium chlorate. 

12. Give the formulas and names of two common compounds of 
sodium with one chemical and one physical property of each. 

13. How much potassium nitrate would be decomposed by 650 
grams of sulphuric acid, and how much nitric acid would be formed? 



CHAPTER XVI. 

THE SIXTH GROUP — HEXADS. 

I. THE CHROMIUM FAMILY. 

Xote. — In the classification of elements according to the periodic 
law (p. 145), oxygen appears as a member of this family. This ele- 
ment has already been considered. 

Chromium : symbol, Cr ; density, 4.78 ; atomic weight, 52 ; valence, 2, 3, 6. 

370. Chromium. — Chromium is a rather rare, almost 
silver-white metal, and is not found free in nature. Its 
chief ore is chromite or chrome iron ore (FeCr 2 G 4 ). It 
forms the green coloring matter of emerald and some 
other minerals. The fused metal is almost as hard as the 
diamond and melts less easily than platinum. At a white 
heat, it combines directly with oxygen or with nitrogen, 
forming, with the latter, a brown chromium nitride. It 
is a good conductor of electricity and is magnetic. The 
presence of from five-tenths to three per cent of this 
metal renders steel ("chromium steel") harder than car- 
bon alone can do. Several chromium compounds are 
somewhat extensively used in the arts. 

371. Chromic Oxides and Acids. — Chromium forms 
three oxides : the monoxide (chromous oxide, CrO) ; the 
sesquioxide (chromic oxide, green oxide of chromium, 
Cr 2 3 ); and the trioxide (chromic anhydride, Cr0 3 ). 

314 



THE CHROMIUM FAMILY. 315 

(a) Chromic trioxide may be obtained by treating potassium di- 
chromate with sulphuric acid. The red crystals thus formed may be 
dissolved in water forming chromic acid (H 2 Cr0 4 ). Dichromic acid 
(H 2 Cr 2 O r ) may be regarded as chromic acid from which water has 
been abstracted. 

Chromium Salts. 

Experiment 249. — To a solution of about 20 grams of potassium 
dichromate slowly add potassium hydroxide until the solution is of a 
pure yellow color. Evaporate two-thirds of the solution to crystalli- 
zation. The red dichromate has been changed to the yellow chromate. 

K 2 Cr 2 7 + 2KOH = 2KoCr0 4 + H 2 0. 

Experiment 250. — Concentrate the remaining -third of the yellow 
solution obtained in the last experiment and slowly add nitric acid 
until the color indicates a change of yellow potassium chromate back 
to red potassium dichromate. 

Experiment 251. — Place a small quantity of potassium chromate in 
a test-tube and add a little concentrated hydrochloric acid. An easily 
recognizable gas will be evolved. From the equation 

K 2 Cr0 4 + 81IC1 = 2KC1 + CrCl 3 + 4H 2 + 3C1, 

show that potassium chromate is a good oxidizing agent. 

Experiment 252. — Repeat the last experiment substituting potas- 
sium dichromate for the chromate. From the equation 

K 2 Cr 2 7 + 14HC1 = 2KC1 + 2CrCl 3 + 7H 2 + 3C1 2 , 

show that potassium dichromate is a good oxidizing agent. 

Experiment 253. — Dissolve 15 grams of pulverized K 2 Cr 2 7 in 
100 cu. cm. of warm water. When the solution has cooled, add 
15 cu. cm. of strong sulphuric acid, and pour it into a porcelain dish 
placed in cold water. When the liquid is cool, slowly stir in 8 cu. cm. 
of alcohol and set the whole aside for a day. At the end of that 
time, crystals of chrome alum will cover the bottom of the dish. 

372. Chromates, etc. — Potassium chromate (yellow 
chromate of potash, K 2 Cr0 4 ) is used in the arts, but the 
potassium dichromate (bichromate of potash, K 2 Cr 2 7 ) is, 



316 THE SIXTH GROUP — HEX ADS. 

by far, the most important of the chromium compounds, 
as it serves as the starting-point in the preparation of 
nearly all of the others. It crystallizes in beautiful gar- 
net-red prisms and is prepared in large quantities from 
chrome iron ore (FeCr 2 4 ). 

(«) Chrome yellow is a lead chroniate (PbCrO^ insoluble in 
water. It is largely used as a pigment. Chrome alum [K2SO4, Cr 2 
(S04) 3 , 24H2O] is a crystallizable double salt used in dyeing, calico- 
printing, and tanning. 

373. The Chromium Family. — The other members of 
this family are the rare metals, molybdenum, neodymium, 
tungsten, and uranium. None of them are found free in 
nature. Molybdenum has a silver- white color and is 
highly infusible. In 1885, Welsbach separated the sup- 
posed element " didymium " into two substances, neodym- 
ium and praseodymium. Some chemists think that the 
so-called didymium consists of a group of nine or more 
elements. Steel that has been hardened by the addition 
of tungsten is used for tools for cutting other hard metals. 
The chief ore of uranium is an impure oxide known as 
pitchblende. The metal is hard and malleable and in 
color resembles nickel ; it is feebly radioactive. The 
uranous salts are green; the uranic salts are yellow. 
Most of the latter have a remarkable power of fluores- 
cence. Uranium yellow (Na 2 U 2 7 ) is largely used to 
give the beautiful yellowish green color to the variety of 
glass known as uranium glass. The uranyl group, U0 2 , 
also acts as a bivalent compound radical in such com- 
pounds as uranyl nitrate and uranyl sulphate. 

(a) The symbols and atomic weights of these elements are given 
in the table of chemical elements printed in the Appendix. Some of 
the family resemblances appear in the table herewith given. 



THE SULPHUR FAMILY. 



317 



Chromium 


CrO 


Cr,0 ;3 





CrO„ 


H 2 Cr0 4 


K 2 Cr 2 7 


Molybdenum 


MoO 


MOgOg 


M0O2 


MoO, 


H 2 Mo0 4 


— 


Xeodvmium 


— 


Nd 2 O a 


— 


Xd0 3 


— 


— 


Tungsten 


— 


— 


WO2 


wo 3 


H 2 W0 4 


— 


Uranium 


— 


Uo0 3 


UOo 


UOo 


— 


Xa 2 U 2 O r 



EXERCISES. 

VI 

1. Write the graphic formula for K 2 Cr0 4 . 

2. The constituents of air are free. Is air a chemical compound? 

3. Is the manufacture of gunpowder a chemical or a physical 
process? Why? The combustion of gunpowder ? Why? 

4. From the formula for chrome iron ore (chromic iron) derive 
the formula for an hypothetical acid of which this ore may be 
regarded as a salt. 

5. If 20 grams of hydrogen are exploded with oxygen, how many 
grams of oxygen are necessary ? How many grams of dry steam will 
be produced ? 

6. You have been given the formula for potassium dichromate. 
Write the formula for dichromic acid. 

7. Write an equation that shows that dichromic acid may be 
regarded as partly dehydrated chromic acid. 

8. When potassium chromate is treated with nitric acid, potassium 
nitrate, potassium dichromate, and water are formed. Write the 
reaction. 

9. Write the formula for some binary compound of trivaleut 
chromium. 

10. Why is " chromium steel " used for burglar-proof safes? 

11. Write in tabular form the name, the atomic and molecular 
symbols, and the atomic weights of 20 elements. 

12. Write the formula for normal sodium phosphate ; for mono- 
sodium phosphate ; for disodium phosphate ; for potassium- hydrogen 
sulphate. 

II. THE SULPHUR FAMILY. 

Sulphur : symbol S ; density, 1.96 to 2.07 ; atomic weight, 32 ; 
valence, 2, 4, 6. 

374. Sulphur. — Sulphur is found in nature free, and in 
combination principally with iron, zinc, and copper. Free 



318 THE SIXTH GROUP — HEXADS. 

sulphur is found in the volcanic regions of Italy and 
Sicily, and in Louisiana, Texas, and some of the Western 
states. It occurs sometimes in the form of transparent 
yellow crystals, but generally mixed with earthy mate- 
rials. It is found in combination with h}~drogen or with 
the metals, as sulphides, and with oxygen and many 
metals, as sulphates. 

(«) Among the native sulphides are hydrogen sulphide (sulphu- 
reted hydrogen, H 2 S), a gaseous constituent of the waters of "sulphur 
springs," lead sulphide (galena, PbS), zinc sulphide (blende, ZuS), 
copper sulphide (chalcocite, CuS), and iron disulphide (pyrite, FeS 2 ), 
etc. Sulphides were formerly called sulphurets. 

(b) Among the native sulphates are calcium sulphate (gypsum, 
CaS0 4 ), barium sulphate (barite or heavy spar, BaS0 4 ), and sodium 
sulphate (Glauber salt, Na 2 S0 4 ). 

(c) Sulphur is a constituent of bone, and of some animal aud 
vegetable tissues. 

(fl) A large part of the sulphur of commerce comes from Sicily. 
Some of the native crystals there found are from 5 to 7 cm. in 
thickness. 

375. Preparation. — Native sulphur is freed from most 
of its earthy impurities near the place where it is found 
and thus fitted for purposes of commerce. The process is 
one of fusion or of distillation. Sulphur may also be ob- 
tained from pyrite by heat. 

(a) One method of obtaining crude sulphur from the native earthy 
material is represented in Fig. 82. The earthy material is trans- 
ferred through an opened slide from the preliminary heater, A into 
the cast-iron pot, A, which is then closed with an iron cover and 
heated by a fire beneath. The sulphur thus vaporized in A passes 
over into closed vessels where it condenses to a liquid. From each 
condenser, B, the liquid sulphur runs out into wooden vessels, K, 
partly rilled with water. The crude ore in the chamber, D, is warmed 
by the heated gases from the fire under A. 



THE SULPHUR FAMILY. 



319 




Fig. 82. 




Fig. 83. 



320 



THE SIXTH GROUP — HEXADS. 



(b) The crude sulphur, provided by the foregoing or some other pro- 
cess, is further purified by distillation. It is melted in a tank, a (Fig. 
83), runs through a pipe into the iron retort, b, where it is vaporized. 
The vapor passes from b into the large brick chamber, C, where it 
condenses. When the walls of C are cold, the sulphur condenses in 
the form of a light powder known as " flowers of sulphur " ; when 
the walls of C are hot, the sulphur condenses to a liquid, and collects 
on the floor of the chamber, whence it is drawn off and run into 
molds to form "roll brimstone." 



Physical Properties of Sulphur. 

Experiment 254. — Put 30 grams of small pieces of dry sulphur into 
a test-tube of about 30 cu. cm. capacity. Hold the test-tube just above 
the lamp-flame (rotating it meanwhile) so that the sulphur melts, form- 
ing a limpid liquid of light yellow color. Heat it hotter and notice 
that it becomes viscid and dark colored. Heat it hotter and notice 
that it becomes almost black. Invert the test-tube and notice that 
the sulphur has become so viscid that it will not run out from the 
tube. Heat it hotter and notice that it again becomes fluid. Heat it 
until it boils and notice that it is converted into a light yellow vapor. 



Experiment 255. 




- Pour half of the boiling sulphur of the last ex- 
periment, in a fine stream, into a large vessel 
nearly full of cold water, keeping the tube in 
motion so as to string out the sulphur; or invert 
a glass funnel in the water and pour the melted, 
sulphur round and round, so as to lay a string 
of sulphur spirally upon the body of the funnel. 
The sulphur when taken from the water will be 
found to have no crystalline structure, to be 
soft, nearly black, and plastic. With filter- 
paper carefully dry a good sample of the plastic 
sulphur without pressing it into a compact mass. 
Carefully weigh the sample and lay it aside for 
a day. Then examine it for change of structure 
and weight. In the meantime, allow the boiling 
sulphur remaining in the test-tube to cool slowly 
and quietly, under close observation. Notice 
that it repasses through the viscid and limpid 



states and finally crystallizes as it solidifies. 




THE SULPHUR FAMILY. 321 

Experiment 256. — Melt 200 grams of sulphur in a clay crucible. 
Allow it to cool until a crust forms over the top. 
Through a hole pierced in this crust, pour out the 
remaining liquid sulphur. When the crucible is cool, 
break it open. It will be found lined with needle- 
shaped crystals. The crucible may be saved by pour- 
ing the melted sulphur into a box of pasteboard or of 
folded paper. (Compare Experiment 24:7.) 

Experiment 257. — Dissolve a piece of sulphur in 
carbon disulphide (CS2). The disulphide will quickly evaporate, 
leaving behind crystals of sulphur that resemble the native crystals. 
Carbon disulphide is very volatile, and its vapor is very inflammable. 
In experimenting with it, see that there is no flame near. 

376. Physical Properties. — Sulphur manifests remark- 
able changes when heated. It melts at 115°, becomes 
dark colored and viscid at 230°, regains its fluidity at 
above 250°, and boils a little below 450°. On cooling, 
these changes occur in inverse order. Its vapor-density 
has been the subject of careful investigation for the sake 
of determining the constitution of its molecule. The 
early determinations of a vapor-density of 96 signify- 
ing a molecule consisting of six atoms, were accepted 
until recent times. In 1860 it was found that above 
860° the vapor-density is only 32, signifying a molecule 
consisting of two atoms. More recently it was found 
that the molecule of sulphur in solution consists of 
eight atoms, and it was inferred that the same mole- 
cule exists in sulphur vapor just above its boiling- 
point. The latest investigations indicate that there 
are only two sulphur molecules (S 8 and S 2 ) and that, 
at the boiling-point, the molecule with eight atoms 
begins to decompose into molecules of two atoms. This 
decomposition is progressive, being complete at about 

SCHOOL CHE31ISTRY — 21 



322 THE SIXTH GJROUP — HEXADS. 

850°. Sulphur is odorless and tasteless, and exists in 
three distinct forms, orthorhombic, monoclinic, and amor- 
phous. 

(a) The crystals of sulphur formed by fusion are monoclinic ; the 
native crystals and those formed by solution and evaporation are 
orthorhombic. Substances which, like sulphur, crystallize under two 
systems are called dimorphous (two-formed). Sulphur is not only 
thus dimorphous, but the plastic variety is amorphous (without 
crystalline form). 

(/>) The orthorhombic form of sulphur is brittle and soluble in 
carbon disulphide, petroleum, or turpentine; it is the stable form 
from low temperatures up to 96°. The monoclinic form is brittle ; it 
is the stable form from 96° to 120°. The form of the crystal seems to 
depend upon the region of stability in which the sulphur happens to 
be. The amorphous form is plastic and insoluble in carbon disul- 
phide. Exposed to the air, it gradually assumes the brittle form at 
ordinary temperatures ; heated to 100°, it changes, and evolves enough 
heat to raise its temperature to 110°. 

Chemical Properties of Sulphur. 

Experiment 258. — Ignite a small piece of sulphur on the bottom of 
an inverted saucer and notice the peculiar blue flame. Cautiously 
observe the odor of the gaseous product. This odor is commonly 
called sulphurous, but it is the odor not of the 
sulphur but of its dioxide (SO.,)- Wet a jnece 
of blue litmus-paper, stick it on the inner sur- 
face of the bottom of a beaker, invert the 
beaker over the burning sulphur, and notice 
the effect of the gas on the litmus. 

Experiment 259. — Mix intimately 4 grams 
of flowers of sulphur and 8 grams of copper 
filings. Heat the mixture in an ignition-tube 
until the elements unite with a vivid combus- 
tion to form copper sulphide (CuS). 

Experiment 260. — In a mortar thoroughly 
mix 3.2 grams of flowers of sulphur and 6.5 
grams of zinc-dust. Take a small portion of 
the mixture on the tip of a spatula-biade and, at arm's length, thrust 




THE SULPHUK FAMILY. 323 

it into a gas-flame. The chemical union of the mixed substances 
produces zinc sulphide. Repeat the experiment using 5.6 grams of 
iron-dust instead of the zinc-dust, and name the product. Compare 
the weights of the sulphur, zinc, and iron used in this experiment 
with the atomic weights of these elements. 

377. Chemical Properties. — Sulphur unites with oxygen 
at the comparatively low temperature of about 250°. It 
enters energetically into union with most of the elements, 
in many cases with the evolution of light. 

378. Uses. — Sulphur is largely used in the manufacture 
of sulphuric acid, vulcanized india-rubber, friction matches, 
gunpowder, and sulphur dioxide. 

379. Tests. — Free sulphur is easily recognized by its 
color, and by the odor of the oxide that is formed when it 
is burned. Combined sulphur may be detected by mixing 
the compound with pure sodium carbonate and fusing the 
mixture before the blowpipe on charcoal. The carbon 
of the charcoal unites with the oxygen of the sulphate 
(for example) forming gaseous carbon dioxide (C0 2 ) 
and leaving the sodium and the sulphur combined as 
sodium sulphide. 

Na 2 S0 4 + 2C = Na 2 S + 2C0 2 . 
When the fused mass is placed on a silver coin and water 
added, a brown stain of silver sulphide is formed on the 
coin. 

EXERCISES. 

1. Why are the ends of friction matches generally dipped in 
melted sulphur or in paraffin? 

2. When sulphur is prepared from pyrite, Fe 3 S 4 is formed. 
Write the reaction. 



324 THE SIXTH GROUP — HEXADS. 

3. By bringing bromine and phosphorus together in the presence 
of water, both phosphoric (H s P0 4 ) and hydrobromic acids are formed. 
(a) What weight of bromine is necessary to yield 5 grains of the 
colorless gas, HBr? (b) What weight of bromine is necessary to 
yield 10 liters of HBr? 

4. Iodine acts upon KClOo, forming potassium iodate and setting 
chlorine free : 

2KC10 3 + I 2 = 2KI0 3 + Cl 2 . 

(a) How much chlorine by weight may thus be freed by 10 grams 
of iodine? (b) How much by volume? 

5. («) How many grams of hydrogen may be prepared by the 
use of 260 grams of zinc? (b) How many liters? (c) How many 
grams of HC1 are necessary? 

6. Can S 2 and S s exist at the same temperature? Explain. 

7. (a) One cubic centimeter of water will yield by electrolysis 
how many grams of free gases? (b) How many cubic centimeters 
of oxygen? (c) How many cubic centimeters of hydrogen ? (7/) The 
explosion of these gases will yield how many cubic centimeters of 
dry steam? 

8. (a) If ozone could be produced from KCIO3, how many 
grams of the former could be produced from 10 grams of the latter? 
(/y) How many liters of the former? 

9. Determine the formula of a compound that has a vapor-density 
of 49, and that contains 2.01 per cent of hydrogen, 32.65 per cent of 
sulphur, and 65.31 per cent of oxygen. 

10. Calomel and corrosive sublimate are each composed of mercury 
and chlorine atoms. Why do the two substances differ, their atoms 
being of the same kind ? 

11. Complete the following equation by inserting the proper 
figures, and correct any error that you find : 

K 2 C10, + HC1 = KC1 + H 2 + CI* 

12. Write with mathematical propriety the names and the molec- 
ular (or the multimolecular) weights of 2HX0 3 , 3CaC0 3 , K 2 CK> 4 , 
2H 3 P0 4 , and Si0 2 , following this model: 

3H 2 O f ; 3[2(1) + 2(16)] = 102, the weight of 3 molecules of hydro- 
gen dioxide. 

380. Hydrogen Sulphide. — Hydrogen sulphide (hydro- 
sulphuric acid, H 2 S) occurs free in certain volcanic gases, 



THE SULPHUK FAMILY. 



325 



and is the characteristic constituent of the waters of " sul- 
phur springs." It is generated by the putrefaction of 
animal matter, causes the peculiar odor of rotten eggs, 
and is a constant constituent of sewer gases. 

Preparation of Hydrogen Sulphide. 

Experiment 261. — Into a gas-bottle, arranged as for the prepara- 
tion of hydrogen, put about 10 grams of iron sulphide (FeS), replace 
the cork snugly, add enough water to seal the 
lower end of the funnel-tube, and place the 
bottle in the ventilating chamber, out of 
doors, or in a good draft of air to carry off 
any of the offensive H 2 S that may escape. 
Let the delivery-tube dip 5 or 6 cm. under 
cold water contained in another bottle, e. 
Add a few cubic centimeters of sulphuric or 
of hydrochloric acid. Bubbles of gas appear 
in e and are absorbed by the water. Add 
acid in small quantities, as in the prepara- 
tion of hydrogen, until the water in e smells 
strongly of the gas. Remove the gas-bottle 
and cork it tightly. Fig. 87. 

381. Preparation. — Hydrogen sulphide may be pre- 
pared by the direct union of its constituents, but it is 
generally prepared by the action of dilute sulphuric or of 
hydrochloric acid upon iron sulphide (ferrous sulphide, 
FeS). The gas may be collected over warm water. 

FeS + H 2 S0 4 = FeS0 4 + H 2 S, or 
FeS + 2HCl =FeCl 2 + H 3 S. 

382. Physical Properties. — Hydrogen sulphide is a 
colorless gas, having a sweetish taste and the offensive 
odor of rotten eggs. At the ordinary atmospheric 
pressure, and at a temperature of — 74°, it condenses 




326 THE SIXTH GROUP — HEXADS. 

to a colorless liquid that boils at — 63.5°, and that solidi- 
fies at — 91° to a white crystalline mass. Its density is 
17, it being thus a little heavier than air. At ordinary 
temperatures, water dissolves a little more than three 
times its volume of the gas. The solution has the pecul- 
iar odor of the gas and a slightly acid reaction. 

Chemical Properties of Hydrogen Sulphide. 

Experiment 262. — Bring a flame to the open mouth of a jar of H 2 S. 
The gas will burn with a pale blue flame, forming water and sulphur 
dioxide, and depositing a slight incrustation of sulphur on the inside 
of the jar. 

Experiment 263. — Attach a drying-tube, containing calcium chlo- 
ride, to the delivery-tube of the gas-bottle. Provide the drying-tube 

with a jet made of glass tub- 
ing. When all of the air has 
been expelled from the ap- 
I paratus, and not till then, hold 
a lighted match to the jet. 
(A mixture of H 2 S and air is 
explosive.) The gas will 
burn with a blue flame. Hold 
a dry bottle over the flame. 
I £ Moisture will condense on 

the sides of the bottle. This 
liquid will redden blue litmus- 
paper. 

|B 2H 2 S + 30 2 = 2H 2 + 2S0 2 . 

Experiment 264. — Bum a 
jet of H 2 S, using the appa- 
ratus arranged as described 
FlG - 88 - in Experiment 28. With blue 

litmus-paper test the liquid that accumulates in the cup. 

Experiment 265. — Heat the glass tube between the drying-tube and 
the jet. The H 2 S will be decomposed and the sulphur deposited od 





THE SULPHUR FAMILY. 327 

the cold part of the tube. The product that now accumulates in the 
cup will not redden blue litmus-paper. The analysis of HgS is here 
followed by the synthesis of water. 

Experiment 266. — Moisten a bright silver or copper coin and hold 
it in a stream of H 2 S. The coin will be quickly blackened by the 
formation of a metallic sulphide. The same effect will follow the 
dipping of the bright coin iuto a water solution of H 2 S. 

Experiment 267. — Write your name in a colorless, water solution 
of lead acetate (sugar of lead). Hold the autograph, before drying, 
in a stream of H2S. The lead snlphide formed renders the invisible 
writing legible. 

Experiment 268. — Make a sketch in the same colorless liquid and 
allow it to dry. At any convenient time, float the paper containing 
the invisible design upon a solution of H 2 S. The figure will " come 
out " promptly. 

Experiment 269. — In separate test-tubes place warm solutions of 
the following substances : 

1. Lead acetate [Pb(C 2 H 3 02)2], diluted. 

2. Mercuric chloride (HgCl 2 ). 

3. Cadmium nitrate [Cd(XOs) 2 ]. 

4. Sodium arsenite (Xa^AsOs) and dilute hydrochloric acid. 

5. Antimony chloride (SbClg). 

6. Zinc acetate [Zn(C 2 H 3 2 ) 2 ]- 

To each tube add a few cubic centimeters of a saturated solution of 
H 2 S. The following precipitates will be found : 

1. Lead sulphide (PbS) ; black. 

2. Mercuric sulphide (HgS) ; red, then black. 

3. Cadmium sulphide (CdS) ; yellow. 

4. Arsenious sulphide (AS2S3) ; yellow. 

5. Antimonious sulphide (SD2S3) ; orange. 

6. Zinc sulphide (ZnS) ; white. 

Write the equation for each of these reactions. Add a dilute acid 
to the contents of each test-tube, and notice what precipitates are 
dissolved. Then treat a dilute solution of zinc sulphate w T ith H 2 S, 



328 THE SIXTH GROUP — HEXADS. 

write the reaction, and explain why there is no precipitate. Add 
a few drops of ammonia-water, and explain why the zinc sulphide 
is precipitated. 

Experiment 270. — Dissolve about a gram of potassium iodide (KI) 
and a few small crystals of iodine in about 10 cu. cin. of water in a 
test-tube. Pass a slow current of FI2S through the solution until the 
latter is decolorized. Hydriodic acid is formed and sulphur is set free. 

H 2 S + I 2 = 2HI + S. 

The potassium iodide is used because, while iodine is only slightly 
soluble in water, it is readily soluble in a solution of an iodide. 

383. Chemical Properties. — Hydrogen sulphide is easily 
combustible, the products of its combustion being water 
and sulphur dioxide, provided there is an excess of oxygen. 

2H 2 S + 30 2 = 2H 2 + 2S0 2 . 

If the supply of oxygen is insufficient, only water and 
free sulphur will be formed, hydrogen having a stronger 
attraction for oxygen than sulphur has. 

2H 2 S + 2 = 2H 2 + 2S. 

Hydrogen sulphide is readily decomposed by many metals 
with liberation of hydrogen and formation of a metallic 
sulphide. 2Ag + H2 g = Ag9§ + Ha 

It is this reaction that causes silverware to tarnish, the 
hydrogen sulphide generally coming from illuminating 
gas and from the products of the combustion of coal. 
Almost all oxidizing agents decompose hydrogen sulphide 
with formation of oxygen-sulphur compounds. It pre- 
cipitates metallic sulphides from solutions of the com- 
pounds of many metals. Its solution reddens blue litmus. 
The gas is very poisonous when breathed, and even when 



THE SULPHUR FAMILY. 



329 



much diluted its respiration is very injurious. Under 
such circumstances, the best antidote is the free inhala- 
tion of pure oxygen preceded by the inhalation of dilute 
ammonia. 

(a) With hydroxides of the metals, hydrogen sulphide yields two 
classes of salts, — sulphides and sulphydrates. 

2KOH + H 2 S = K 2 S + 2H,0 
KOH + H 2 S = KHS + H.O. 

The salts that appear in the products of these illustrative reactions 
are potassium sulphide (K 2 S) and potassium hydrosulphate (KHS). 

384. Volumetric Composition. — The composition of hy- 
drogen sulphide may be ascertained by heating metallic 
tin in a known volume of the gas. The gas will be de- 
composed, the sulphur combining with the tin as tin 
sulphide and the hydrogen being set free. The volume 
of hydrogen will be the same as that of the hydrogen 
sulphide decomposed. When a platinum-wire spiral is 
electrically heated to redness in a known volume of Irydro- 
gen sulphide, the gas is decomposed. The volume of the 
hydrogen will again be the same as that of the hydrogen 
sulphide. Careful analyses have proved that the com- 
position of this gas may be expressed by the following 
diagram : 



*l + 


H 

1 


+ 


S 

32 



H,S 

34 



385. Uses and Tests. — Hydrogen sulphide is very ex- 
tensively used in the chemical laboratory as a reagent, 
forming sulphides that are characteristic (in color, solu- 
bility, or some other easily recognized property) for cer- 
tain metals or groups of metals. It is easily detected by 



330 THE SIXTH GROUP — HEX ADS. 

its odor, or by holding in it a strip of paper wet with an 
aqueous solution of lead acetate. 

Note. — Hydrogen sulphide was formerly called sulplmreted hy- 
drogen. Hydrogen persulphide (H 2 S 2 ) lias been prepared as a yellow, 
transparent, oily liquid. 

386. Carbon Disulphide. — Carbon disulpbide (CS 2 ) is 
prepared synthetically on a large scale by passing sulphur 
vapor over glowing coke or charcoal. 

C 2 + 2S 2 = 2CS 2 . 

Caution. — In performing experiments with CS2, see that there is 
no flame near. 

Properties of Carbon Disulphide. 

Experiment 271. — Put a few drops of CS2 into each of four small 
test-tubes. Into the first tube put a little powdered sulphur; into 
the second, a few crystals of iodine ; into the third, a 
very small piece of phosphorus; into the fourth, a 
little water. Notice the solubility of the sulphur, 
iodine, and phosphorus in CS 2 , and the insolubility of 
CS2 in water. 

Experiment 272. — Wet a block of wood and place 
a watch-crystal upon it. A film of water may be seen 
under the central part of the glass. Half fill the 
crystal with CS2 and rapidly evaporate it by blowing 
over its surface a stream of air from the lungs or 
from a small bellows. So much heat is rendered 
latent in the vaporization that the glass is firmly 
frozen to the wooden block. 

Experiment 273. — Into a glass cylinder pour a few 
drops of CS 2 . In a few moments the cylinder will be 
filled with a heavy vapor. Thrust into the cylinder 
the end of a glass rod, heated not quite to redness. 
The vapor will be ignited. 

30 2 + CS 2 = CO2 + 2S0 2 . 




THE SULPHUR FAMILY. 331 

387. Properties. — Ordinary carbon disulphide is a 
liquid of light yellow color and offensive odor. Its vapor 
is injurious to animal and vegetable life and exceedingly 
inflammable. As it is heavier than water and insoluble 
therein, it is easily preserved under water. It is diather- 
manous, has a highly refractive effect upon light, evapo- 
rates rapidly at ordinary temperatures, and boils at about 
46°, yielding a heavy vapor that ignites at about 150°, 
and that forms an explosive mixture with air. Pure 
carbon disulphide is colorless and has an agreeable odor 
resembling that of chloroform. 

388. Uses. — Carbon disulphide is used as a solvent for 
phosphorus, iodine, sulphur, and many resins and oils. It 
is used in the extraction of fats and oils, in the cold pro- 
cess of vulcanizing caoutchouc, and largely for the extermi- 
nation of vermin, and as a solvent for rubber in making 
rubber cement. 

EXERCISES. 

1. Write the reaction for Experiment 261. 

2. When metallic tin is heated in H 2 S, the gas is decomposed. 
The sulphur unites with the tin. (a) Xame the solid and gaseous 
products, (b) How will the volume of this gaseous product compare 
with that of the decomposed gas ? 

3. When a spiral of platinum wire is heated in an atmosphere of 
H 2 S, the gas is decomposed with the deposition of solid sulphur. 
What volume of hydrogen can thus be set free from a liter of H 2 S ? 

4. The reaction resulting from passing a current of H 2 S through 
an aqueous solution of bromine is as follows : 

H 2 S + Br 2 = 2HBr + S. 

(a) What volume of H 2 S is needed to yield 4 liters of HBr? 

(b) What weight of bromine will thus combine with 10 grams of 
H 2 S? 

5. Why was 6H instead of 3H 2 written into the equation near the 
bottom of page 262 ? 



332 THE SIXTH GROUP — HEXADS. 

6. (a) How many liters of oxygen will unite with 20 liters of NO 
to form X0 2 ? (b) How many each of oxygen and NO to form 30 
liters of N0 2 ? 

7. Arsenic vapor is 150 times as heavy as hydrogen, (a) What 
is the molecular weight of arsenic ? Explain. (6) The atomic weight 
of arsenic is 75. How many atoms are there in an arsenic molecule? 

8. (a) What name would you apply to a substance that has only 
one kind of atoms ? (b) One that has two kinds? (c) One that has 
three kinds? 

9. State Avogadro's law. Define chemistry. 

10. What weight of sulphur in 10 liters of sulphur vapor under 
normal pressure at 500° ? At 1050° ? 

11. How much zinc sulphide will be formed by the precipitation 
of 10 grams of zinc chloride by hydrogen sulphide ? 

12. What volume of hydrogen sulphide, at 0° and 760 mm., will be 
required for the precipitation mentioned in Exercise 11? 

13. An analysis of acetic acid shows that it contains about 40 per 
cent of carbon, 6.67 per cent of hydrogen, and 53.33 per cent of oxy- 
gen. The vapor-density of the acid is found to be about 30. Deter- 
mine from these data the formula for acetic acid. 

14. What is the valence of sulphur in hydrogen sulphide ? 

15. Write in tabular form the names, molecular symbols, and 
molecular weights of 10 binary compounds that you have studied. 

389. Sulphur Oxides. — Sulphur and oxygen unite to 
produce two acid-forming oxides (or anhydrides) symbol- 
ized as S0 2 and S0 3 . These unite with water to form the 
acids symbolized as H 2 S0 3 and H 2 S0 4 . 

(a) In addition to these, we have sulphur sesquioxide (S 2 O g ), which 
has no corresponding known acid; hvposulphurous acid (H 2 S0 2 ), 
which has no corresponding known oxide; sulphur peroxide (S 2 O r ) ; 
and the thionic acids (§ 403). Sulphur sesquioxide is a rare com- 
pound, and easily decomposes into sulphur dioxide and sulphur. 

390. Sulphur Dioxide. — This oxide of sulphur (S0 2 ) is 
known by the various names of sulphurous oxide, sulphu- 
rous anhydride, sulphurous acid gas, and sulphuryl. 



THE SULPHUK FAMILY. 



333 



Preparation of Sulphur Dioxide. 

Experiment 274. — Put 20 or 30 grams of small bits of copper (Cu) 
and 60 cu. cm. of strong sulphuric acid into a flask and apply heat. 
The gas that is evolved may be purified by passing it through water 
in a wash-bottle, b (Fig. 90), and then collected by downward displace- 
ment or over mercury. It may be recognized by its familiar odor. A 
solution of copper sulphate (blue vitriol, CuS0 4 ) remains in the flask. 

2H 2 S0 4 + Cu = CuS0 4 + 2H 2 + S0 2 . 

Experiment 275. — When an aque- 
ous solution of the gas is desired, 
the above experiment may be modi- 
fied by substituting charcoal for the 
copper, and absorbing the gas in 
water as shown at c. 

2H 2 S0 4 + C = 2S0 2 + 2H 2 + C0 2 . 

If these mixed gases are passed 
through water in a series of Woulffe 
bottles (Fig. 29), most of the sulphur 
dioxide and very little of the carbon 
dioxide will be absorbed. Such a 
solution is often wanted in the 
laboratory. p IG q 0# 

391. Preparation. — For industrial purposes, sulphur 
dioxide is generally prepared by burning sulphur or some 
sulphide in the air. When thus prepared, it is mixed 
with nitrogen from the air. When the pure anhydride is 
wanted, it is generally prepared from strong sulphuric 
acid by heating it with copper, mercury, or carbon, as 
illustrated by the preceding experiments. 




Properties of Sulphur Dioxide. 

Experiment 276. — From the generating flask, a (Fig. 90), pass the 
S0 2 through a bottle or tube packed in ice ; then dry the cool gas with 



334 



THE SIXTH GROUP — HEXADS. 




sulphuric acid or calcium chloride; then pass the dry gas through a 
U-tube packed in salt and pounded ice. The SO a will condense to a 
liquid at the low temperature thus pro- 
duced. If the U-tube has good glass 
stop-cocks, as shown in the figure, the 
liquid S0 2 may be sealed and preserved. 
If the two arms of a common U-tube 
have been previously draw n out to make 
a narrow neck upon each, the expensive 
stop-cocks may be dispensed with ; after 
the condensation of the SO2, these necks 
may be fused with the blowpipe flame 
and the liquid thus sealed for preservation. 

Experiment 277. — Add a few drops of the aqueous solution of SO2 
to a weak solution of potassium permanganate. The red color of the 
latter will disappear, owing to its reduction by S0 2 - 

Experiment 278. — Burn some sulphur under a bell-glass within 
which are some moist, bright-colored flowers. The flowers will be 
bleached. The color may be partly restored by 
dipping some of the flowers into dilute sulphuric 
acid and others into ammonia- water. 

Experiment 279. — Partly fill each of two glasses 
with a fresh infusion of purple cabbage. Add a 
little of the aqueous solution of S0 2 . The bleach- 
ing action is not very manifest. To each, add 
cautiously, drop by drop, a solution of potassium 
hydroxide (caustic potash, KOH) ; the color will 
disappear. To the contents of one glass, add a 
little strong sulphuric acid; a red color appears. 




Fig. 92. 
To the other add 



more of the solution of the hydroxide ; a green color appeal's. 

Experiment 280. —Lower a lighted taper into a jar of S0 2 . Does 

this gas support combustion ? 

Caution. — The next three experiments should be performed under 
a ventilating hood with a good draft. 

Experiment 281. — Pour some of the liquid S0 2 upon the surface of 
mercury contained in a capsule, and, by means of a bellows, blow a 
current of air over it. The mercury will be frozen. 



THE SULPHUR FAMILY. 335 

Experiment 282. — If you have a thick, platinum crucible, heat it 
red-hot and pour some of the liquid S0 2 into it. The dioxide will 
assume the " spheroidal state," like that of the globules of water some- 
times seen upon the top of a hot stove, the temperature of the liquid 
being below its boiling-point. If, now, a little water is poured in, the 
SO2 will be instantly vaporized by the heat taken from the water, 
which therefore at once becomes ice. By some dexterity, the lump of 
ice may be thrown out o£ the red-hot crucible. 

Experiment 283. — Wrap the bulb of an alcohol thermometer in 
cotton-wool and pour some of the liquid SO2 upon it. The change of 
sensible into latent heat effected by the vaporization of the dioxide 
produces a diminution of temperature and the thermometer falls, per- 
haps as low as — 60°. 

392. Properties. — Sulphur dioxide is a transparent, 
colorless, irrespirable, suffocating 'gas. Under ordinary 
conditions, it is neither combustible nor a supporter of 
combustion. It has a density of 32, being more than 
twice as heavy as air. It bleaches many colors, not by 
destroying the coloring matter, as chlorine does, but by 
uniting with it to form unstable, colorless compounds. 
When, by the action of chemical agents, the sulphur 
dioxide is set free from the colorless compounds thus 
formed, the color reappears. This oxide condenses to a 
liquid at — 16° under the ordinary atmospheric pressure, 
or at the ordinary temperature under a pressure of three 
atmospheres. The liquid has a density of 1.43, boils at 
— 8°, and vaporizes rapidly in the air at the ordinary 
temperature, producing great cold. It solidifies when 
cooled below — 76 d . 

(a) Sulphur dioxide has a strong affinity for oxygen. If these dry 
gases are conducted over hot platinum-sponge or platinized asbestos, 
sulphur trioxide is formed. 

2S0 2 + 2 = 2SO a . 



336 



THE SIXTH GROUP — HEXADS. 



The Winckler or " contact " method, by which large quantities of 
sulphuric acid are made, is based on this reaction. 

(b) An aqueous solution of SO2 slowly absorbs oxygen from the 
air, yielding sulphuric acid (H2SO.J. Write the reaction in complete 
molecules. Some other agents effect a similar change more promptly, 
thus : 

S0 2 + 2H 2 + T 2 = H2SO4 + 2HI. 

(c) The composition of sulphurous anhydride is represented by the 
following diagram : 





16 


+ 


O 

16 


+ 


s 

32 



S02 

64 



393. Uses and Tests. — Sulphur dioxide is largely used 
in the manufacture of sulphuric acid and for bleaching 
straw, silk, woolen goods, and wood-pulp for the manu- 
facture of paper. It is also used as an antichlor for the 
purpose of removing the excess of chlorine present in the 
bleached rags from which paper is made, and as an anti- 
septic. When free, it is easily detected by its familiar 
odor and by its blackening a paper wet with a solution of 
mercurous nitrate. 



394. Sulphur Trioxide. — When dry oxygen and dry 
sulphurous anhydride are mixed and passed over heated 
platinum-sponge or platinized asbestos, they combine, 
forming dense fumes of sulphur trioxide (sulphuric oxide, 
sulphuric anhydride, S0 3 ). When these fumes are con- 
densed in a dry, cool receiver, they form white, silky, 
fiber-like crystals resembling asbestos. Sulphur trioxide 
may be prepared more easily by gently heating Nord- 
hausen acid (§ 401) and condensing the vapor given off, 
as in the method above described. When perfectly dry, 



THE SULPHUR FAMILY. 337 

it does not exhibit any acid properties and may be 
molded with, the fingers without injury to the skin. It 
has so great an attraction for water that it can be pre- 
served only in vessels hermetically sealed. It unites with 
water with a hissing sound and the evolution of much 
heat, forming sulphuric acid. 

S0 3 + H 2 = H 2 S0 4 . 

395. Sulphurous Acid. — Sulphur dioxide is freely solu- 
ble in water, forming sulphurous acid (hydrogen sul- 
phite, H 2 S0 3 ). At 40° this liquid is decomposed into 
water and sulphur dioxide ; when it is cooled below 5°, 
it yields a crystalline hydrate of sulphurous acid with a 
composition of H 2 S0 3 , 14H 2 0. On standing, it absorbs 
oxygen from the air and changes to sulphuric acid 
(H 2 S0 4 ). As it is dibasic, it gives rise to two series of 
sulphites (§ 94). The term "sulphurous acid" is fre- 
quently applied to sulphur dioxide, but such use of the 
term is incorrect. 

396. Sulphuric Acid. — Sulphuric acid (hydrogen sul- 
phate, oil of vitriol, H 2 S0 4 ) seldom occurs free in nature, 
but its salts, especially those of calcium and barium, are 
abundant. Sulphuric acid is to the chemical arts what 
iron is to the mechanical arts; it enters, directly or in- 
directly, into the preparation of nearly every substance 
with which the chemist deals. It has been said that the 
commercial prosperity of any country may be well meas- 
ured by the quantity of sulphuric acid that it uses. 

397. Preparation. — Sulphuric acid is formed by the 
addition of water to sulphur trioxide. The water may be 

SCHOOL CHEMISTRY 22 



338 



THE SIXTH GROUP — HEXADS. 



added at the time of the formation of the anhydride or 
subsequently. For this purpose, the sulphuric anhydride 
is formed by the oxidation of sulphurous anhydride by 
means of nitrogen oxides or acids, or by the method of 
oxidation described in 8 394. 




(«) In a bottle having a capacity of 1 liter or more, burn a bit of 
sulphur. In the atmosphere of SO2 thus formed, place a stick (or a 
glass rod carrying a tuft of gun cotton) that has been 
dipped in strong nitric acid. Red fumes of nitrogen 
dioxide will appear. The red fumes show that the 
nitric acid has been robbed of part of its oxygen. 

2IINO3 + S0 2 = H 2 S0 4 + 2X0 2 . 

In the presence of moisture, SO2 is able to reduce (i.e., 
\ J to take oxygen from) IIN0 2 , HXO3, N ft Os, or N0 2 . In 
^^^ the process just described, the SO2 reduced the acid ; 
Fig. 93. the acid 0X1 dized the S0 2 . 

(b) The manufacture of H 2 S0 4 may be prettily represented by the 
following lecture-table process : A large glass globe or flask is filled 
with air or oxygen 
and provided with 
five tubes. One 
tube connects it 
with a flask that 
furnishes a current 
of S0 2 ; another 
connects it with a 
second flask or 
bottle, that fur- 
nishes a current of 
nitric oxide ; the 
third connects it 
with a flask that 
furnishes a current FlG - 9*- 

of steam; by the tube, d, a supply of air or oxygen is admitted, from 
time to time, into the globe. The fifth tube, e, allows the escape of the 
waste products of the reaction ; it may be connected with an aspirator. 




THE SULPHUR FAMILY. 



339 



(1) Nitric oxide enters the globe and takes oxygen from the air. 
The ruddy fumes of nitrogen peroxide are seen. 

(2) On admitting a current of 80 2 , the red fumes of nitrogen 
peroxide disappear and white "leaden-chamber crystals" form on 
the walls of the globe. The N0 2 has been reduced and the S0 2 
oxidized. 

(3) On admitting steam, the crystals disappear, and dilute H 2 S0 4 
collects at the bottom of the globe. 

(4) If air is admitted, red fumes again appear and the process may 
be repeated. 

(c) In the manufacture of this acid on the commercial scale, S0 2 and 
nitrogen oxides are generally formed by burning crude sulphur, pyrite 
(FeS 2 ), or blende (ZnS) in kilns provided for that purpose, as shown at 
S in Fig. 95. The quantity of air admitted is carefully regulated. From 




the kilns the S0 2 and other gases are drawn through the apparatus 
by the draft of a large chimney. They are carried first into the 
leaden Glover tower, G, which is filled with coke that is drenched with 
nitrosyl-sulphuric acid from the Gay-Lussac tower, L. If the nitro- 



340 THE SIXTH GRADE — HEXADS. 

gen oxides are not supplied in sufficient quantity by the reaction of 
sodium nitrate and H 2 S0 4 in the furnaces, liquid nitric acid is 
allowed to trickle down over the coke in G. The II 2 S0 4 formed 
in this Glovt-r tower is drawn off below, while nitrogen trioxide, air, 
and an excess of SO2 pass on to the lead-lined chambers, A, B, and C, 
in succession. In each of these chambers the gases meet steam, and 
the oxidation and the union with water continue. These lead cham- 
bers are sometimes 30 meters long, 6 or 7 meters wide, and about 5 
meters high, having thus a capacity of about a thousand cubic 
meters. They are supported by a wooden framework, carried by 
pillars of brick or iron. The H 2 S0 4 formed in the chambers accu- 
mulates on the floor. The process is conducted so that this " chamber 
acid" has a density of 1.55, as a stronger acid absorbs the nitrogen 
oxides. After leaving the lead chambers, the excess of nitrogen 
oxides is absorbed by concentrated H 2 S04 in the Gay-Lussac tower, 
while the nitrogen escapes. The "chamber acid," which contains 
64 per cent of H 2 S0 4 , is then concentrated in the " denitrating," or 
Glover tower, where it is mixed with the " nitrated acid " from the 
Gay-Lussac tower and exposed to the influence of the hot gases as 
they pass from the kilns into the chambers. If not yet sufficiently 
concentrated, the acid from the Glover tower is evaporated in leaden 
pans until it has a density of 1.7 and contains 78 per cent of HoS0 4 . 
If concentrated beyond this point, the hot acid attacks the lead of 
the pans. Lead is used for this apparatus because it is the cheapest 
metal not attacked by dilute sulphuric acid. In this form the acid is 
technically called brown oil of vitriol, as it is slightly colored by 
organic impurities. It is largely sold for a great variety of pur- 
poses. Further concentration and purification are carried on in glass 
retorts of from 75 to 150 liters capacity, or in large platinum stills 
until the liquid contains 98 per cent of H2SO4 and has a density of 
upwards of 1.8. The strongest acid may be concentrated in cast-iron 
stills, as when its density is greater than 1.8 it has little action on 
iron. 

(d) Although we have no reason to think that some of the reac- 
tions in the manufacture of H 2 S0 4 are not simultaneous, we may, 
with propriety, trace them as if they were really consecutive. Sev- 
eral such explanatory series of reactions have been written out. One 
of these is herewith given, not as a didactic statement of what actu- 
ally takes place, but as a theoretical exposition of what may take 
place. 



THE SULPHUR FAMILY. 341 

(1) 4FeS 2 + 110 2 = 8S0 2 + 2Fe 2 3 , or S + 2 = S0 2 . 

(2) 2HN0 3 + 2S0 2 + H 2 = 2H 2 S0 4 + X 2 3 . 

(3) S0 2 + N2O3 = S0 3 + 2X0. 

(4) S0 3 + H 2 = H0SO4. 

(5) 2N0 + 2 = 2X0 2 , or 4X0 + 2 = 2X 2 3 . 

The X0 2 and the N 2 3 formed by these reactions are absorbed by 
the concentrated H 2 S0 4 in the Gay-Lussac tower, combining chemi- 
cally to form nitrosyl-sulphuric acid. 

2H 2 S0 4 4- X 2 3 = 2H(XO)S0 4 + H 2 0. 

This nitrosyl-sulphuric acid is pumped back to the Glover tower, 
where it comes into contact with steam, whereby H 2 S0 4 and X 2 3 
are formed. 

2H(XO)S0 4 + H 2 = 2H 2 S0 4 + X 2 3 . 

(e) It is thus seen that most of the oxygen nsed for the oxidation 
of the S0 2 comes from the air admitted to the chambers through the 
kiln. The part taken in the process by the nitrogen oxide is very 
interesting, it acting as a carrier of oxygen from the air to the S0 2 . 
Theoretically, but not practically, a single molecule of HX0 3 or of 
XO would be sufficient for the manufacture of an unlimited amount 
of H 2 S0 4 , as may be seen by repeating the equations above (omitting 
the second) in a series continue^ to any extent desired. But, since 
air is used instead of pure oxygen, the nitrogen thus introduced into 
the chambers has to be removed, and, in its passage out, sweeps away 
some of the nitrogen oxides, which then have to be supplied anew. 

(/) The lead chambers for this method of manufacturing H 2 S0 4 
are expensive, as is the niter used. The Winckler method previously 
mentioned (§ 392, a) requires a considerable investment for platinum- 
sponge, but it requires no niter and yields a concentrated acid, pure 
without distillation. It is gradually replacing the chamber process 
where the strongest acid is required. 

Properties of Sulphuric Acid. 

Experiment 284. — Place 27 cu. cm. of water in a graduated tube. 
Slowly add 73 cu. cm. of H 2 S0 4 . When the mixture has cooled, 
notice that its volume is about 92 cu. cm. instead of 100 cu. cm. 

Caution.- — In mixing H 2 and H 2 S0 4 , pour the acid into the 
water, not the water into the acid. If the lighter liquid is poured on 



342 THE SIXTH GROUP — HEXADS. 

top of the heavier, it will float there and great heat will be developed 
at the level where they come into contact. This heat might form 
steam of sufficient tension to burst through the heavier liquid above 
and do damage by scattering the acid. When the above directions 
are followed, the heavy acid mixes with the water as it falls 
through it. 

Experiment 285. — Place 30 cu. cm. of water in a beaker of about 
250 cu. cm. capacity. Into this, pour 70 cu. cm. of concentrated 
H2SO4 in a fine stream. Stir the mixture with a test-tube containing 
alcohol or ether, colored with cochineal or other coloring matter. The 
liquid in the test-tube will boil. Holding the test-tube in a pair of 
nippers, ignite the escaping vapor. The test-tube may be closed with 
a cork carrying a delivery-tube, and the jet ignited. It w r ill give a 
voluminous flame. With a chemical thermometer, take the tempera- 
ture of the liquids before and after mixture. If the test-tube stirrer 
contains water instead of the more volatile liquids mentioned, the 
water will boil. 

Experiment 286. — Dip a splinter of w T ood into H 2 S0 4 . It will be 
charred as if by fire. 

Experiment 287. — Repeat Experiment 1. The black mass consists 
partly of carbon, and partly of half-carbonized sugar. The concen- 
trated acid has so great an affinity fpr w T ater, that it removes the con- 
stituents thereof from the carbon with which they are combined to 
form sugar (C12H32O11). It acts similarly with most compounds in 
which carbon is united with hydrogen and oxygen. 

398. Properties. — The sulphuric acid of commerce is 
largely known as oil of vitriol, because it is of an oily 
consistency and was originally made by distilling green 
vitriol (ferrous sulphate). It has a density of about 1.82. 
It generally contains, as impurities, lead sulphate from 
the chambers and evaporating pans, and arsenic from the 
pyrite. For most purposes, however, it answers as veil 
as the " H 2 S0 4 , C.P.," or chemically pure acid. The pure 
acid is a colorless, oily, very corrosive liquid with a den- 
sity of 1.84 at the ordinary temperature. It has a very 



THE SULPHUR FAMILY. 343 

remarkable attraction for water, the combination being 
marked by a condensation of volume and the evolution of 
much heat. It may be mixed with water in all propor- 
tions. When exposed to the air at ordinary temperatures, 
it does not vaporize but absorbs water from the atmos- 
phere, thus increasing both its weight and volume. On 
account of this hygroscopic action, it should be kept in 
well-stoppered bottles. It is dibasic. 

Sulphuric acid removes water from many organic sub- 
stances, completely charring some, like sugar and woody 
fiber, and breaking others, as alcohol and oxalic acid, into 
new compounds. It is one of the most energetic acids 
known. Diluted with 1000 times its bulk of water, it 
still reddens blue litmus. Because of its higher boiling- 
point, it liberates most of the other acids from their salts. 
If the concentrated acid comes into contact with the skin, 
it will (unless washed off at once) produce a wound diffi- 
cult to heal and likely to leave a scar. Its corrosive 
action is destructive to clothing with which it comes in 
contact. Even the dilute acid (unless it is soon neutral- 
ized with ammonia) will eventually destroy fabrics with 
which it comes in contact. Internally, it acts as a corro- 
sive poison, the best antidote for which is a solution of 
baking-soda, or strong soapy water. 

399. Uses. — Sulphuric acid is used as a drying agent 
for gases, in the preparation of most of the other acids, in 
the manufacture of soda, phosphorus, and alum, in the 
preparation of artificial fertilizers, in the refining of petro- 
leum, in the manufacture of glucose, in the processes of 
bleaching, dyeing, etc. In fact, there is scarcely an art 



344 THE SIXTH GROUP — HEXADS. 

or trade in which, in some form or other, it is not used, it 
being employed directly or indirectly in nearly all impor- 
tant chemical processes. It is the most important chemical 
reagent Ave have and is made in immense quantities. 

400. .Tests. — The most convenient test for free sul- 
phuric acid is the charring of organic substances. A 
paper moistened with a natural water containing the free 
acid and then dried at 100° will be completely charred. 
The acid or solutions of its salts give a white precipitate 
with barium chloride. This precipitate is insoluble in 
hydrochloric acid. 

401. Nordhausen Acid. — Nordhausen acid (disulphuric 
acid, fuming sulphuric acid, pyrosulphuric acid, H 2 S 2 () 7 ) 
is prepared by dissolving sulphur trioxide in ordinary 
sulphuric acid, or by the distillation of dried iron sul- 
phate (green vitriol, FeS0 4 ), in earthen retorts. It 
is a heavy, oily liquid with a density of 1.89. It fumes 
strongly in the air and hisses like a hot iron when 
dropped into water. It is used chiefly for dissolving 
indigo. 

(a) The name, Nordhausen acid, is due to the fact that it was for- 
merly prepared in Nordhausen, Saxony. At the present time the 
acid comes almost wholly from Bohemia. The propriety of the term 
" disulphuric acid," is shown by the formula, H2O, 2SO3. It is easily 
decomposed : H 2 S 2 7 + heat = S0 3 + H2SO4. 

402. Hyposulphurous Acid. — Hyposulphurous acid 
(H 2 S0 2 ) is a very unstable, yellow liquid with powerful 
reducing properties. Its salt, sodium-hydrogen hyposul- 
phite (NaHS0 2 ), is used for the reduction of indigo in 
dyeing and calico-printing. 



THE SULPHUR FAMILY. 345 

403. Thionic Acids. — Besides the foregoing, there is a 
series of sulphur acids, the corresponding oxides of which 
are unknown. 

Thiosulphuric acid H2S2O3 

Dithionic acid H 2 So() 6 

Trithionic acid H0S3O6 

Tetratbionic acid H2S4O6 

Pentathionic acid H2S5O6 

None of these acids is of technical importance, but the 
sodium salt of the first of the series, commonly called 
sodium hyposulphite (Na 2 S 2 3 ), is, on account of its sol- 
vent action on the halogen salts of silver, largely used in 
photography and in the extraction of silver from its ores. 

(a) The thiosulphuric acid is better known by the misnomer of 
" hypos ulphurous " acid, which properly designates the compound 
symbolized by HoS0 2 . In similar manner the thiosulphates (e.g., 
sodium thiosulphate, Na^SoOg) are commonly, but improperly, spoken 
of as " hyposulphites." The word " thionic " comes from the Greek 
name for sulphur. 

404. Selenium and Tellurium. — These are rare ele- 
ments, having properties in general very similar to those 
of sulphur and forming compounds analogous to those of 
sulphur. The resistance that selenium offers to an elec- 
tric current is much diminished by the action of light. 
This property has been utilized in the construction of the 
photophone, and the element thus endowed with added 
interest and importance. (See Appendix, § 1.) 

(a) The name selenium is from the Greek word meaning the 
moon, and the name tellurium is from the Greek word meaning the 
earth. 

405. The Sulphur Family. — The resemblances between 
the members of this family are as well marked as are those 



346 THE SIXTH GROUP — HEXADS. 

of the halogens. As the atomic weight increases, the 
chemical activity diminishes, selenium being about mid- 
way between sulphur and tellurium. Their densities, 
melting- and boiling-points, show a similar gradation. 

(«) Some of the chemical resemblances of the members of this 
group are easily visible in the following table : 



H 2 S 


H 2 Se 


H 2 Te 


FeS 


FeSe 


FeTe 


S0 2 


Se0 2 


Te0 2 


S0 3 


Se0 3 (?) 


TeO s 


H2SO3 


H 2 Se() 3 


H 2 Te0 3 


H 2 S0 4 


H 2 Se0 4 . 


H 2 Te0 4 


(C 2 H S ) 2 S 


(C 2 H 5 ) 2 Se 


(C 2 H 5 ) 2 Te 


(C 2 H 5 )HS 


(C 2 H 5 )HSe 
EXERCISES. 


(C 2 H 5 )HTe 



1. (a) What is the molecular weight of S0 2 ? (b) The density of 
the gas? (c) Its percentage composition? 

2. H 2 S and S0 2 are often found in volcanic gases. When they 
come into contact, they decompose each other. Write an equation 
explaining the occurrence of native sulphur in volcanic regions. 

3. Why can not H 2 S0 4 be used for drying H 2 S? 

4. (a) How much HX0 3 can be formed from 308 grams of KXO, ? 
(b) How much H 2 S0 4 will be required ? (c) What will be the yield 
of KHS0 4 ? 

5. Write the graphic symbol for II 2 S0 4 : (a) representing sul- 
phur as a dyad ; (b) as a hexad. 

6. Write the graphic symbol for H 2 S 2 O r , introducing S0 2 twice 
as a bivalent radical. (H 2 S20 7 = anhydrosnlphuric acid.) 

7. The symbol for potassium sulphate is K 2 S0 4 ; that for lead 
sulphate is PbS0 4 . (a) What is the valence of potassium? (b) Of 
lead? 

8. How would you write the symbol of a binary compound con- 
taining a dyad and a triad? 

9. How much HN0 3 will just neutralize 1200 grams of ammo- 
nium hydroxide? 



THE SULPHUR FAMILY. 347 

10. (a) How much XH 3 may be formed from 42.8 grams of 
NH 4 C1? (b) How much CaH 2 Q 2 must he used? 

11. (a) What volume of chlorine may be obtained from 1 liter 
of dry HC1 ? (b) What weight ? 

12. AV r hen aeriform water and chlorine are passed through a porce- 
lain tube heated to redness, hydrochloric acid and oxygen are formed, 
(a) Write the reaction in molecular symbols, (b) What volume of 
oxygen may be thus obtained from 2 liters of steam ? (c) How will 
the volume of the acid compare with that of the oxygen ? (d) In 
what simple way may the oxygen be freed from mixture with the 
acid ? 

13. (a) From 100 grams of KCIO3, how many grams of oxygen 
may be obtained ? (b) How many liters ? 

14. Water and nitrogen are among the products formed when 
NH 4 C1 and NaN0 2 are heated together in a flask. Write the reaction. 

15. (a) 1 mix hydrogen and chlorine, and expose the mixture to 
sunlight. What happens ? (b) I add NH 3 to the product just formed. 
What is the name of this second product ? 

16. (a) What weight of sulphur would be required to produce a 
ton of sulphuric acid ? (b) What weight of steam would be needed ? 
(c) What volume of air, if all the oxygen is used ? 

17. What weight of iron pyrite (FeS2) would be required to pro- 
duce a ton of sulphuric acid? 

18. Write in tabular form the names, molecular symbols, and 
molecular weights of 10 ternary compounds that you have studied. 

19. When anhydrous magnesium chloride, MgCl 2 , is burned in air, 
a white powder and a gas are produced. The powder is magnesium 
oxide ; the gas will color blue a strip of paper wet with a solution of 
potassium iodide and starch. Write the reaction. 

20. When barium oxide, BaO, is gently heated to dark redness in 
the air it is changed to the dioxide, Ba0 2 . At a bright red heat this 
decomposes into barium oxide and oxygen. How may these facts be 
utilized ? 

21. Symbolize three molecules of arsenic, two of cadmium, five of 
oxygen, two of phosphorus, and four of mercury. 

22. How many grams of pure cream of tartar (KHC 4 H 4 O ) are 
required to make baking-powder with 1000 grams of pure baking- 
soda (NaHC0 3 ) ? 



CHAPTER XVII. 

THE EIGHTH GROUP. 

I. THE IRON FAMILY. 

Note. — The five elements of Group 7 were considered in 
Chapter VIL See § 148, (e) and (/). 

Iron : symbol, Fe; density, 7.8 ; atomic weight, 56 ; valence, 2, 3, 6. 

406. Occurrence. — Iron, the most important of all the 
metals, is seldom found native. Metallic iron of meteoric 
origin has been found. This element is widely distributed, 
traces of it being found in the blood of animals, in the 
ashes of plants, in spring, river, and ocean waters, and, in 
fact, in nearly all natural substances. Its ores are numer- 
ous and abundant. 

(a) The most important iron ores are hematite (Fe 2 3 ) ; limonite 
or brown hematite (Fe 2 3 , 3H 2 0) ; magnetite or magnetic iron 
(Fe 3 4 ) ; siderite (FeC0 3 ), and clay ironstone or black-band iron- 
stone, which is a carbonate ore containing clay or sand with carbona- 
ceous substances and generally found as nodules or bands in the coal 
measures. 

(b) The value of an iron ore often depends more upon the nature 
of its impurities than upon its percentage of iron. When iron is 
spoken of, a compound of iron and carbon is usually meant. 
Chemically pure iron is not a commercial product, and has properties 
quite different from those of commercial iron. 

Preparation of Pure Iron. 

Experiment 288. — Place about 15 grains of pulverized FegOa in the 
bulb of the tube, c. Pass a current of dry hydrogen through the bulb- 
348 




THE IHON FAMILY. 349 

tube. When the air has been driven from the apparatus, heat the 
oxide to redness. When it has been reduced to a black powder of 
metallic iron, remove the 
lamp and allow the contents 
of the bulb to cool in a cur- 
rent of hydrogen. 
Fe 2 3 + 3H 2 =Fe 2 + 3H 2 0. 

407. Pure Iron. — 

Pure iron may be made 
by heating iron oxide 
in a current of hydro- 
gen. The black powder 
prepared in the preceding experiment may be set on fire 
by a lighted splinter. It oxidizes so easily that it will 
take fire if emptied from the bulb-tube into the air while 
it is still hot. When hammered, pure iron is silver- white, 
soft, and tenacious. It melts at about 1800°, is permanent 
in dry air, and rusts rapidly in moist air. 

408. Commercial Iron. — All forms of commercial iron 
contain carbon, and usually manganese, phosphorus, sili- 
con, and sulphur. The proportion of carbon present 
largely determines the quality of the metal and the use 
to which it may be applied. When the amount of carbon 
is so small that the iron can not be hardened by sudden 
cooling (less than two-tenths per cent), the metal is 
called wrought iron. When carbon is present in such an 
amount that the metal can be hardened by sudden cooling 
and can be tempered (i.e., from about two-tenths per cent 
to about two per cent), the metal is called steel. The 
hardness and hardening power of the steel increase with 
its carbon contents. Soft steel for boiler-plate, sheet 
steel, and the like, contains about two-tenths per cent ; 



350 THE EIGHTH GROUP. 

rail steel and structural steel, from three-tenths to five- 
tenths per cent ; and tool steel, above six-tenths per cent 
of carbon. Iron that is too high in carbon contents to 
be tempered (containing more than about two per cent of 
carbon) is called cast iron or pig iron. 

409. Metallurgy of Iron. — Almost all the iron of com- 
merce is made by smelting and reducing the ores in a 
blast-furnace. This consists of an upright shaft, A, from 
sixty to a hundred feet high, made of steel plate, and with 
a lining from three to five feet thick and made of the 
most refractory fire-brick. The furnace is wider in the 
middle than at the top or bottom, thus allowing an easy 
descent of the material. Near the bottom are from six to 
fourteen apertures (tuyeres) for forcing in hot air. At 
the bottom is the hearth or crucible with an opening near 
its top for drawing off the slag, and a narrow slit near its 
bottom for tapping off the molten metal. The top of the 
blast-furnace is closed by a massive cup-and-cone arrange- 
ment that is opened only when a fresh " charge " of mate- 
rials is to be dropped into the furnace from the hopper 
above. Trucks containing the materials, mixed in proper 
quantities, are lifted by large elevators, E, to the charg- 
ing platform, P, at the mouth of the furnace. The 
"burden," as the mixture is called, is dumped from the 
trucks into the hopper. When the hopper is tilled, 
the cone is lowered, and the charge falls into the furnace. 
Just below this cone is the opening of a large steel pipe 
through which the combustible gases that would other- 
wise escape are led, in part to the boilers used in making 
steam for the blowing engines, and in part to the cylindri- 



THE IRON FAMILY. 



351 



cal towers or hot-blast stoves, B, C, etc. Air is admitted 
to these stoves and the gases are burned. The stoves are 




nearly filled with loosely built brickwork which is thus 
heated red-hot. While several of these stoves are being 
thus heated, air is forced through another previously 



352 THE EIGHTH GROUP. 

heated. The hot brickwork raises this air to a very high 
temperature, after which the hot air is forced through the 
circular main blast that surrounds the furnace, and thence 
through the tuyeres into the lower part of A. When the 
brickwork is thus cooled, the air-blast is transferred to 
another stove, the several stoves being alternately heated 
by the combustion of the gas from the blast-furnace, and 
cooled by the air on its way to the blast-furnace. The 
heat and fuel that would otherwise be lost from the top 
of A are thus utilized in the lower part of A. 

410. Pig Iron. — The iron ores and the coke necessary 
for smelting them are charged together almost continu- 
ously at the top of the blast-furnace. Most iron ores con- 
tain silica. To render this silica fusible, limestone is 
added to the charge. The limestone acts upon the silica 
and, with it and the other impurities of the ores, forms 
silicates that constitute the slag. As the coke falls to the 
lower part of the furnace and meets the incoming hot air, 
it is burned. 2C + o 2 = 2C0 . 

As the carbon monoxide thus formed rises through the 

charge, it reduces the downcoming hot iron oxides to the 

metal. 

Fe 2 8 + 3CO = 2Fe + 3CO a . 

Only about half of the carbon monoxide is thus used. 
The other half is led from the top of the blast-furnace to 
the stoves, where it is burned to furnish heat for the air- 
blast as already described. 

At the high temperature of the lower part of the 
stack, the reduced iron unites chemically with part of the 



THE IRON FAMILY. 



353 



carbon of the coke to form a compound that contains 
about four and one-half per cent of carbon and two per 
cent of silicon. At the hottest part of the furnace this 
more easily fusible compound melts and settles to the 
bottom of the furnace ready to be drawn off and run into 
sand or iron molds. The bars thus formed constitute pig 
iron. This iron can not be welded or tempered, and is 
more brittle and less strong than other forms of iron. 

(«) Pig iron includes white cast iron, gray cast iron, and several in- 
termediate varieties called mottled cast iron. White cast iron contains 
nearly all its carbon in chemical union. When it is dissolved in hydro- 
chloric or in sulphuric acid, various hydrocarbons are formed that 
give a disagreeable odor to the hydrogen evolved. In gray cast iron, 
part of the carbon crystallizes out in cooling, forming graphite, which 
is left in the form of black scales when the iron is dissolved in an 
acid. White cast iron contracts on solidifying; gray cast iron ex- 
pands on solidifying and is, therefore, the better adapted for foundry 




Fig. 98. 
school chemistry 23 



354 



THE EIGHTH GROUP. 



use. Spiegeleisen is a variety of white cast iron containing about 30 
per cent of manganese. It is very hard and crystalline and is used in 
various processes of steel manufacture. When it contains 50 to 80 per 
cent of manganese, it becomes granular aud is called ferromanganese. 

411. Wrought Iron. — To convert the product of the 
blast-furnace into soft or wrought iron, the pig iron is 
melted in a furnace, mixed with oxide of iron, and stirred 
or puddled, whereby the carbon is burned away and the 
other impurities are oxidized to a slag ; this slag protects 
the iron from further oxidation. The loss of carbon raises 
the melting-point of the iron, and the metal becomes less 
fluid. The pasty mass or " bloom " is then removed from 
the furnace and freed of its slag, and welded into a solid 
mass by hammering or squeezing. The iron made in this 
way is the most nearly pure of the commercial varieties. 
It is soft and malleable, and may be welded, and rolled or 
hammered into the shape required. 

(a) A puddling furnace is shown in elevation in Fig. 98 and in 
section in Fig. 99. The charge of pig iron and, generally, a quantity 
of iron-scale or other iron oxide are placed in the bed, h, separated 
from the fire-grate by the fire-bridge, b, and from the chimney by the 
flue-brid 




Fig 



THE IRON FAMILY. 



355 



412. Steel. — Steel is intermediate between cast iron and 
wrought iron in respect to properties and chemical com- 
position. It contains from two-tenths to two per cent of 
carbon. Its most characteristic property is that of acquir- 
ing remarkable hardness by heating and quickly cooling 
as by plunging into water. Steel thus hardened can not 
be worked with a file and is very brittle and elastic. The 
hardness and brittleness are lessened by tempering, which 
process consists in heating the steel to a temperature be- 
tween 200° and 400° and then cooling it quickly. 



413. The Cementation Process. — Fifty years ago the 
only method of making 
steel was to decarbonize 
cast iron in the puddling 
furnace and then to recar- 
bonize the wrought iron 
in the cementation furnace. 
This furnace contains two 
boxes, cc, made of fire-clay. 
In these boxes, bars of 
wrought iron are packed in 
soot or powdered charcoal. 
Six or seven tons of iron 
are put into each box. A 

».-.■■,.,, , n , Fig. 100. 

lire is built on the hearth, g, 

and the boxes are kept at a red heat for from seven to 

ten days. At the end of the process, it is found that the 

metal has become finer grained, more brittle, more fusible, 

that its surface has a blistered appearance, whence the 

name, " blister steel," and that carbon has penetrated the 




356 



THE EIGHTH GIIOUP. 



metal, although the iron has not been melted or the carbon 
vaporized. The bars are then taken out and welded, or 
melted and cast into shape. 



414. The Bessemer Process. — In this process, so named 
for its inventor, steel is made by decarbonizing cast iron 
by a current of air forced through the melted metal in a 
vessel called the converter. The converter is made of 
iron j)lates lined with infusible material. The bottom is 
a shallow wind-box, e, from which numerous small open- 
c ings lead into the converter. 

The vessel is supported upon 
trunnions, one of which, i, is 
hollow and connected with the 
wind- or tuyere-box. "When the 
converter has been turned uj)on 
its trunnions until the line, ac, 
is horizontal, melted cast iron 
is run through the mouth into 
the belly, abc. The air-blast is 

WM^MMmmMk,, % then turned on and the converter 

FlG " 101, raised into an upright position, 

the compressed air bubbling through the molten metal, 
burning out the carbon and silicon, and combining with 
part of the iron. This combustion in the converter causes 
an intense heat that keeps the iron melted despite its 
approach to the less easily fusible condition of wrought 
iron. During this time, the flame that rushes from the 
mouth of the converter is accompanied by a magnificent 
display of sparks due to the combustion of iron particles. 
After six or eight minutes, the exact moment being indi- 




THE IKON FAMILY. 357 

cated by the appearance of the flame, the converter is 
turned until the melted iron leaves the tuyere openings 
uncovered and the air-blast is stopped. The decarbonized 
iron is now recarbonized by the addition of a carefully 
determined quantity of spiegeleisen. The molten mass is 
poured into molds, and the cast steel worked up under 
the hammer or in the rolling mill. In about twenty 
minutes, from ten to twenty tons of cast iron have been 
converted into steel. 

(a) All the movements of the converter, ladle, cranes, etc., are 
produced by hydraulic power, and controlled by a workman at "the 
piano," as the assemblage of wheels and levers is called. 

(b) Steel might be produced by stopping the oxidation before all 
of the carbon of the cast iron had been burned out. But the diffi- 
culties arising from too nearly complete oxidation and the practical 
impossibility of making successive " blows " yield the same quality 
of steel led to the adoption of the present plan. Bessemer steel is 
largely used in the construction of railway tracks, bridges, etc. 

415. The Siemens-Martin or Open-hearth Steel Process. — 

In this process, iron high in carbon (pig iron), and iron 
low in carbon (soft scrap iron and steel) are fused to- 
gether in the proportions proper to produce such a carbon 
contents in the resulting metal as will yield the desired 
kind of steel. In practice, part of the carbon of the pig 
iron is removed in a gas-fired furnace by the oxidizing 
flame, or by its reaction with the iron rust (oxide) on the 
surface of the scrap iron or of added iron ore. 

Fe 2 + 3C = 2Fe + SCO. 

Because of the very high temperature necessary to melt 
soft iron, this method did not become a commercial possi- 
bility until, about 1860, Siemens invented a process for 



358 



THE EIGHTH GROUP. 




THE IKON FAMILY. 



359 



returning to the furnace a large part of the heat of the 
exit furnace gases, i.e., a heat regenerative process. 

The open-hearth steel furnace consists of a rectangular chamber, 
A, lined with highly refractory fire-brick and having a concave sand 
bottom, B, upon which the metals are melted. The Wellman 
machine for mechanically charging the metals and fluxes into the 
furnace is shown at G i and the valves for reversing the direction of 
the fuel gases are shown at H. 

The regenerative chambers for heating the fuel gas and air before 
their admission to the chamber, A, are usually built below the level 
of the working platform and at the back of the furnace. They are 
not represented in Fig. 102, but their construction is shown in Fig. 103. 
These chambers, M, N, 0, P, are built in pairs and tilled with loosely 
set brick that are alternately heated by the hot gaseous products of 
combustion on their way from the furnace to the chimney-stack, E, 
and cooled by the fuel gas and air on their way to A. 



< ' f\ v 








!. | \ 




• ■:■. :■'■// 








/ 




JMB 


LjeitJjil^jji 






VP^ 


^r 


-^^ 


y^ 


^-~ 


o 










=== 


:;; :'. -.';.'. 


Pr^ 




= 


pLz= 


— - 


n 




|H 


■.:■::.': 


'^M 


Hi 


ggg 



;> 



r \ ■] i \ f -j r 



Fuel gas being admitted by a duct to the bottom of M, and air 
being similarly admitted to the bottom of N, both are heated by con- 
tact with the hot brick -work, pass thence through separate flues to 
the chamber, A, and there develop a much higher temperature than 
they would if they had been supplied cold. The hot exit products 



360 THE EIGHTH GROUP. 

pass out through similar flues at the other end of A, heating the brick 
work in O and P as they pass on to E. As the brick work in .1/ and 
N are thus soon cooled, the direction of the gases is reversed by the 
valves at H, admitting fuel gas through P and air through O, while 
the exit gases escape to E by way of M and N. In practice, this re- 
versal is made about every fifteen minutes. 

If the sand bottom, B, is made of silica sand, the method is called 
the acid open-hearth process. This process does not remove the 
phosphorus and sulphur that are often present as injurious impurities 
in the ores or metals used. If the sand bottom is made of calcium 
and magnesium oxides, and lime is added to the molten charge, the 
method is called the basic open-hearth process. This process does 
remove the phosphorus and sulphur if such impurities are present. 

When the metal has been melted and refined to its desired purity, 
and brought to the desired carbon contents, it is tapped or poured, 
with the accompanying slag, through the spout, C, into the ladle, D, 
from the bottom of which the pure, slag-free, white-hot metal is 
tapped into an ingot mold, F. When the ingots are cooled to a full 
red heat, they are rolled into billets or other desired shapes. The 
process affords a convenient method of utilizing scrap and, with or 
without modification, is largely used. 

416. Crucible Steel. — A very fine quality of steel is 
made for edge-tools by fusing, in graphite crucibles, a fine 
quality of wrought iron with powdered charcoal. The 
crucibles are closely covered and heated in a coke fire. 
The steel is cast into ingots, and worked into bars under 
the hammer. For very hard metal-cutting tools, the steel 
is alloyed with a small quantity of tungsten, molybdenum, 
or vanadium. 

417. Malleable Iron Castings. — Intermediate between 
cast iron and wrought iron is an article known in com- 
merce as malleable iron. Small castings are made of 
white cast iron for a great variety of purposes, such as 
for harness, wagons, agricultural implements, etc. These 



THE IRON FAMILY. 361 

castings are packed with iron-scale or oxide in " annealing 
boxes " and then heated to a high temperature. The car- 
bon of the cast iron is thus removed in great part and the 
material changed from white, hard, .and brittle cast iron 
to black, soft, and tough malleable iron. Articles thus 
made are nearly as tough as they would be if made of 
wrought iron and much less expensive. 

418. Oxides of Iron. — Iron forms three well-known 
oxides : ferrous oxide (iron monoxide, FeO), ferric oxide 
(iron sesquioxide, Fe 2 3 ), and ferrosoferric oxide (mag- 
netic oxide of iron, Fe 3 4 ). The ferric and magnetic 
oxides are found native as iron ores. 

(a) Ferrous oxide may be prepared by heating ferrous oxalate in 
a closed vessel or by passing hydrogen over Fe^Os heated to 300°. If 
exposed to the air within a few hours after its preparation, it oxidizes 
so rapidly as to take fire. 

(b) Ferric oxide is one of the most important iron ores. This 
oxide is prepared artificially for use as a paint. A fine variety is 
known as jeweler's rouge, and is used for polishing glass and metals. 
Another artificial variety is called crocus, and is also used for polish- 
ing metals. 

(c) Ferrosoferric oxide is found in large quantities as the richest 
of iron ores. Many specimens attract iron and are called lodestones. 
Scale oxide is chiefly Fe 3 04. We may consider Fes0 4 as a mixture 
or compound of FeO and FeoOs. 

Ferric Hydroxide. 

Experiment 289. — Cover a teaspoonf ul of fine iron filings with 
3 or 4 times its volume of dilate sulphuric acid. When the evolu- 
tion of hydrogen ceases, pour off the clear liquor, add a few drops 
of strong nitric acid, and boil the liquid. The yellowish red color 
is due to the presence of ferric sulphate. Add XH 4 OH to the 
solution and shake the liquids together. A red precipitate of ferric 
hydroxide will be formed ; it may be collected upon a filter. 



362 THE ErGHTH GROUP. 

419. Iron Hydroxides. — Ferrous hydroxide [Fe(OH) 2 ] 
is obtained by treating a solution of a pure ferrous salt 
with potassium or sodium hydroxide in absence of air. 
The precipitate thus formed is an unstable, white powder, 
which rapidly oxidizes with change of color, evolution of 
heat and, sometimes, incandescence when exposed to the 
air. Ferric hydroxide [Fe(OH) 3 ] is prepared by precipi- 
tating a moderately dilute solution of a ferric salt (e.g., 
FeCl 3 ) with an excess of ammonia-water. When freshly 
prepared, it is one of the best antidotes for arsenic. 

420. Iron Sulphides. — Iron and sulphur form two 
well-known compounds, iron monosulphide (ferrous sul- 
phide, FeS) and iron disulphide (FeS 2 ). Iron monosul- 
phide is formed by direct union of its constituents. It is 
generally prepared by gradually throwing a mixture of 
three parts of iron filings and two parts of sulphur into a 
red-hot crucible. It is the cheapest source of hydrogen 
sulphide and, hence, very important. Iron disulphide 
occurs widely distributed in nature as pyrite (or iron 
pyrites). It is largely used in the manufacture of sul- 
phuric acid. 

Mordants. 

Experiment 290. — Dip a piece of cotton cloth into a solution of 
nut-galls and allow it to dry ; dip it into a solution of green vitriol 
and hang it up in a moist atmosphere. It will be permanently colored 
by the precipitation of an insoluble iron tannate. 

421. Iron Salts. — Iron forms two well-defined series of 
salts. In the ferrous series, the iron atom acts as a dyad 
as it does in ferrous oxide. In the ferric series, the iron 
atom acts as a triad as it does in ferric oxide. These 
relations clearly appear in the following table : 



THE IRON FAMILY. 363 

Chlorides. Nitrates. Sulphates. 

Ferrous . . . FeCl 2 Fe(X0 3 ) 2 I FeS0 4 

Ferric .... FeCl 3 I Fe(X0 3 )s I Fe 2 (S0 4 ) 3 . 

(o) Solutions of ferrous salts readily absorb oxygen ; unless an ex- 
cess of acid is present, they are thereby oxidized to ferric salts which 
are precipitated. They, therefore, act as powerful reducing agents, 
and are largely used as such in the laboratory and the arts. The ferric 
salts are readily reduced to the corresponding ferrous compounds. 

(b) Ferrous sulphate (green vitriol, FeSO-t, 7H 2 0) is made in 
immense quantities by exposing pyrite to the action of the atmos- 
phere, as an incidental product in the manufacture of copper sul- 
phate, or by dissolving iron in dilute sulphuric acid. It is largely 
used in the arts. Ferric nitrate is prepared by dissolving iron in 
nitric acid. It is largely used as a mordant in dyeing and calico- 
printing. Ferrous carbonate (FeC0 3 ) is found as an iron ore. 

Iron Cyanides. 

Experiment 291. — Half fill each of two test-glasses with a very 
dilute solution of ferrous sulphate, and each of two other glasses with 
a similar solution of ferric sulphate. Prepare a dilute solution of 
potassium ferrocyanide (EUCeXeFe) and one of potassium ferricyanide 
(K 3 C 6 X 6 Fe). Add a drop of the ferrocyanide to one of the solutions 
of ferric sulphate ; a deep blue precipitate will be formed and color the 
liquid. In similar manner, add potassium ferrocyanide to a solution 
of ferrous sulphate ; no such deep blue color will appear. In similar 
manner, add potassium ferricyanide to ferrous sulphate ; the deep 
blue color will appear. In similar manner, add potassium ferri- 
cyanide to ferric sulphate ; no such color will appear. In the names 
of these cyanides the pupil will notice contractions for ferrous and 
for ferric. When, in this experiment, an -ous and an -ic compound 
were brought together, a characteristic blue color was formed. When 
two -ous and two -ic compounds were brought together, no such color 
was produced. These potassium -iron cyanides act thus with all ferrous 
and ferric salts and may, consequently, be used as tests to detect the 
presence of these salts in any solution or to distinguish between them. 

Experiment 292. — Soak a piece of cotton cloth in a solution of fer- 
ric sulphate, and then dip it into an acidulated solution of potassium 
ferrocyanide. Prussian blue will be precipitated upon the cloth and 
will color it. 



361 THE EIGHTH GROUP. 

422. Iron Cyanides. — Iron unites with cyanogen to 
form ferrous and ferric cyanides. The most important 
iron cyanides, however, are double compounds. When 
crude potash (K 2 C0 3 ) is fused with nitrogenous organic 
matter, such as horn, feathers, dried blood, leather clip- 
pings, etc., in the presence of iron filings, and the fused 
mass is leached with water, and the liquid is evaporated, 
large yellow crystals are formed. These crystals are 
potassium ferrocyanide (K 4 Cy 6 Fe) better known as yellow 
prussiate of potash. This compound is important as it 
serves as the point of departure for the preparation of 
nearly all the cyanogen compounds. It may also be 
formed by the addition of a ferrous salt to an aqueous 
solution of potassium cyanide. The tendency to form 
this salt is so great that metallic iron is rapidly dissolved 
when heated in such a solution of potassium cyanide. 
When a current of chlorine is passed into a solution of 
potassium ferrocyanide, the reaction yields potassium fer- 
ricyanide (K 3 Cy 6 Fe) or red prussiate of potash. The 
class of compounds known as Prussian blues are chiefly 
compounds of ferrous and ferric cyanides, generally united 
with potassium. 

423. Ferric Acid. — Acting with a valence higher than 
that manifested in any of the compounds so far men- 
tioned, iron enters into composition to form ferric acid, 
H 2 Fe0 4 . Potassium ferrate (K 2 Fe0 4 ) is a salt of this 
acid. 

EXERCISES. 

1. Name the compounds symbolized as follows: FeBro, FeBr 3 , 
K 4 (CN) 6 Fe, Fe 2 (S0 4 ) 3 . 



THE IRON FAMILY. 



365 



2. A certain iron oxide has a molecular weight of 232 and contains 
27.6 per cent of oxygen. What is its formula ? 

3. How many tons of pure iron maybe made from a thousand tons 
of iron ore containing 90 per cent of pure hematite (Fe 2 Os) ? 

4. (a) What weight of iron sulphide will be needed to yield 1 
liter of hydrogen sulphide ? (b) How much air will be required to 
burn the H 2 S ? 

5. What weight of marble is needed to convert a ton of soda crys- 
tals into bicarbonate of soda ? 

6. How many liters of air will be necessary to burn a liter each of 
marsh-gas, olefiant gas, and acetylene? 

7. The vapor density of XH 4 C1 is one-fourth its molecular weight. 
Why is it said to be abuormal? Can you suggest an explanation of 
the variation? 

8. Give the names and atomic weights of the elements represented 
by the following symbols : Fe, Alg, Hg, Zn, Ca, C, CI, I, P, K, X, Xa, 
S, Br, Fl, H, Pb, 6, Al, Sb, Si. 



H 2 



Cl 2 



2HC1. 



Name of molecules 


Hydrogen 


Chlorine 


Hydrochloric acid 


No. of molecules 


1 


1 


2 


Molecular weights 


2 


71 


36.5 


Total weights 


2 


71 


73 


Gaseous volumes 


2 unit volumes 


2 unit volumes 


4 unit volumes 


Laboratory exp. 


500 cu. cm. 


500 cu. cm. 


1 liter 



9. According to the above or a similar schedule, write out the 
following equations : 

(a) 2H 2 + 2C1 2 = 4HC1 + 2 . 

(b) 2CO + 2 = 2C0 2 . 

(c) C0 2 + C (solid) = 2CO. 

(d) 2XH 3 = X 2 + 3H 2 . 

(e) 2NH 3 + 3C1 2 = N 2 + 6HC1. 
(/) NH 4 XOs (solid) = N 2 + 2H 2 0. 

(y) MnO a + IHC1 = MnCl 2 + Cl 2 + 2H 2 0. 

(h) S0 2 + 2H 2 + Cl 2 = H 2 S0 4 + 2HC1. 

(0 2MnO a + 2H 2 S0 4 = 2MnSQ 4 + 2H 2 f 2 . 



366 THE EIGHTH GROUP. 

10. Write the formula for uranyl sulphate. 

11. Write the graphic formula for ferric acid. 

12. Complete the following equations : 

S0 3 + HoO = 

H 2 S0 4 + NaOH = Xa 2 S0 4 + 

H 2 S0 4 + NaOH = XaHSO, + 

13. Sulphur trioxide may be obtained by heating concentrated 
sulphuric acid with phosphoric anhydride. Write the reaction. 

14. Complete the following equations : 

Na 2 S0 3 + O = 
S0 2 + O = 

15. Tell clearly how you would separate the nitrogen from the 
oxygen of the air, and make a sketch of the apparatus that you 
would use. 

Nickel : symbol, Ni ; density, 8.9 ; atomic weight, 58.6 ; valence, 2, 3. 

424. Nickel. — Nickel is almost always associated with 
cobalt in either terrestrial or extra-terrestrial matter. It 
is a lustrous, white metal, ductile, malleable, magnetic, very 
hard, and susceptible of a high polish. It can be welded. 
It is largely used for electroplating articles of iron and 
steel to protect them from rusting. It is also used in 
making alloys. The United States five-cent coin is made 
of an alloy composed of twenty-five per cent nickel and 
seventy-five per cent copper. German silver is an alloy 
of nickel, copper, and zinc. A small proportion of nickel 
combined with steel forms an alloy of so great strength 
that it is used in armor-plate for war-ships. There are two 
important sources of nickel, — a sulphide and a silicate. 
The sulphide occurs in large quantities near Sudbury, 
Ontario. A silicate of nickel and magnesium, called 
garnierite, occurs in New Zealand. These two deposits 
at present furnish practically all the nickel of commerce. 



THE IRON FAMILY. 367 

(a) The oxides of nickel are the monoxide (nickel oxide, NiO) and 
the sesquioxide (nickelic oxide, Ni20 3 ). Nickel salts are derived 
from the monoxide. 

Cobalt. 

Experiment 293. — Into a small loop of platinum wire fuse some 
borax until it forms a clear glass. Into this fuse a minute portion of 
some cobalt compound. The glass will be colored blue. This forms 
a very delicate test for cobalt. 

Experiment 294. — Partly fill a test-tube with a concentrated solu- 
tion of bleaching-powder. Add a small quantity of cobalt sesquiox- 
ide and heat gently. A brisk effervescence takes place. Test the gas 
evolved with a glowing splinter. The calcium hypochlorite contained 
in the bleaching-powder is, under the catalytic influence of the C02O3, 
decomposed. Write the reaction. 

Experiment 295. — Prepare an aqueous solution of cobaltous chlo- 
ride (C0CI2) by dissolving CoO or C02O3 in hydrochloric acid. Make 
a drawing with this nearly colorless solution. Heat the sketch to 
about 150° C; it will appear blue. Breathe upon it; the blue color 
will disappear. 

Experiment 296. — To 2 cu. cm. of the pink solution of CoCl 2 in a 
test-glass, add an equal quantity of sodium silicate or " water glass," 
well diluted so as to be thin. A blue precipitate appears. 

C0CI2 + Na 2 Si0 3 = 2XaCl + CoSi0 3 ,'or 
2CoCl 2 + Na 4 Si 5 0i 2 = 4XaCl + Co 2 Si 5 Oi 2 . 

Cobalt : symbol, Co ; density, 8.6 ; atomic weight, 58.6 ; valence, 2, 3. 

425. Cobalt. — Cobalt is not found free, except in mete- 
oric matter. Its ores are not widely distributed. The 
metal may be obtained from an artificially prepared oxide 
by reduction with hydrogen, or from a chloride by igni- 
tion. It is harder than iron and melts more easily. It 
is magnetic, malleable, and very tough. When pure, it is 
silvery-white. 



368 THE EIGHTH GROUP. 

(a) Cobalt has three oxides, — the monoxide (cobaltous oxide, 
CoO), the sesquioxide (cobaltic oxide, C02O3), and an intermediate 
compound, cobaltous-cobaltic oxide (Co 3 4 ) which corresponds to the 
magnetic oxide of iron. There are also two series of salts, — the co- 
baltous and the cobaltic. Their peculiar property of appearing pink 
in combination with water and changing to a more easily percep- 
tible blue when dried leads to their use in the preparation of " sympa- 
thetic inks." Cobalt is principally used as an oxide for coloring glass 
and as a blue color in porcelain-painting. 

EXERCISES. 

1. What is the difference between hard w r ater and soft water? 

2. Read the following, naming each symbolized substance by its 
full systematic name: FeS0 4 , 7H 2 is pale gTeen; MnS0 4 , 7H 2 is 
pale pink; CoS0 4 , 7H 2 is bright red; XiS0 4 , 7H 2 is bright 
green ; and CrS0 4 , 7H 2 is pale blue. 

3. («) How is hydrogen sulphide made, and what are its prop- 
erties V (6) What is meant by oxidizing agents, and what by reduc- 
ing agents ? 

4. Manganese dioxide and hydrochloric acid are heated together. 
Give the properties of the gas evolved. 

5. In § 129 (d) it is stated that when a solution of manganous 
chloride is treated with lime we have the reaction : 

MnCl 2 + Ca(OH) 2 = Mn(OH) 2 + CaCl 2 . 

Whence comes the calcium hydroxide that appears as a factor in the 
equation ? 

6. When a thin stream of sulphuric acid flows into a retort filled 

with broken bricks heated to redness, the following reaction takes 

place : 

H 2 S0 4 = S0 2 4-H 2 + 0. 

(a) What weight and (h) what volume of oxygen can be thus pre- 
pared from 50 grams of H 2 S0 4 , C.P. ? (C.P. - chemically pure.) 

7. Which is the correct symbol for nickel hvdroxide, XiOII or 
Ni(OH) 2 ? 

8. (a) Write the symbol for cobaltous hydroxide, (b) For # co- 
baltic hydroxide. 

9. Write the equation for the preparation of sulphurous acid from 
its anhydride and water. 



THE IRON FAMILY. 369 

10. Write the formula for the potassium salt of the hydroxide of 
manganese heptoxide. What is the name of the salt? 

11. How many grams of nickel may be made from a kilogram of 
nickel sulphide (NiS) ? 

12. Name the substances symbolized as follows : K 2 S0 3 , C 12 H 22 O n , 
Si0 2 , C 2 H 4 2 , K 2 S0 4 , NaHS0 3 , CH 4 , KHS0 4 , H 4 Si0 4 . 

13. Complete the following equations : 

S + O + heat = 
H 2 S0 3 + O = 

14. Describe the electrolysis of water, and tell how you would de- 
termine which of the products is oxygen. 

15. Compute the percentage composition of ferric acid. 

Copper : symbol, Cu ; density, 8.95 ; atomic weight, 63.1 ; valence, 1, 2, 4. 

426. Source. — Copper was probably the first metal 
used by man, as it is often found native and then requires 
no metallurgical treatment. Native copper is found in 
quantities of commercial importance only in the Lake 
Superior mines (Keweenaw Point, northern Michigan). 

(a) Among the more important of the copper ores are cuprite 
or red copper ore (Cn 2 0), malachite (CuC0 3 + Cu0 2 H 2 ), azurite 
(2CuC0 3 -f CuO„H 2 ), chalcocite or copper glance (Cu 2 S), and chal- 
copyrite or copper pyrites (CuFeS 2 ), the last being the most impor- 
tant. About nine-tenths of the world's supply of copper comes from 
sulphide ores. 

427. Preparation. — The reduction of copper oxides 
and carbonates is easily effected by smelting with carbon. 
The sulphides are roasted to volatilize some of the con- 
stituents and to oxidize others. The roasted ore is then 
fused with a silicate, whereby a slag containing most of 
the iron is formed, and nearly pure copper and iron sul- 
phide are obtained. This sulphide is then treated by 
forcing a blast of air through it while in a molten state 

SCHOOL CHEMISTRY — 24 



370 THE EIGHTH GROUP. 

and in a vessel called a Bessemer converter such as is used 
in the manufacture of steel. The sulphur and iron are 
burned, leaving an impure copper. This is purified by 
partly oxidizing it in a reverberatory furnace or by 
electrolysis. 

428. Properties. — Copper is a reddish metal, hard, 
very tenacious, and highly malleable and ductile. Ex- 
cepting silver, it is the best-known conductor of heat and 
electricity. It is not much affected by air or by most of 
the acids at the ordinary temperature. It is readily solu- 
ble in dilute nitric acid, and is dissolved in hot sulphuric 
acid. It melts at about 1200°. 

(a) Copper forms two distinct series of compounds, the cuprous 
and the cupric ; e.g. : — 



Monad copper. 


Dyad copper. 


f CuCl 

Cuprous | CuBr 

1 Cu 2 Q 


Cupric ■ 


CuCl 2 
CuBrs 
CuO 



429. Uses. — Copper is largely used for many familiar 
purposes. On account of its toughness, it is used in the 
manufacture of small tubular boilers, for coating the 
bottoms of ships, etc. ; on account of its conductivity, it 
is employed in ocean cables and for other electric uses. 
Brass, bronze, bell-metal, and other copper alloys are of 
great technical importance and are, perhaps, used more 
than copper itself. 

(a) Brass, an alloy of zinc and copper, is of especial value because 
it does not contract when solidifying and, therefore, takes the mold 
perfectly, and because it takes a high polish. Bronze, an alloy of tin 
and copper, has much more strength than most other copper alloys. 



THE IRON FAMILY. 371 

Copper Oxides. 

Experiment 297. — Hold a bright copper coin obliquely in the small 
flame of a gas- or an alcohol-lamp. Move it to and fro and notice the 
beautiful play of iridescent colors. Cool the coin in water and notice 
its coating of red oxide. Heat the coin again, holding it in the hot, 
oxidizing part of the flame, just above the luminous cone, and notice 
that it becomes coated with a black oxide. Quickly cool the coin in 
water and notice that the black coat scales off and reveals the red 
coat beneath. 

Experiment 298. — Place a small quantity of dry copper nitrate 
upon a piece of porcelain and heat it until red fumes are no longer 
given off. A black copper oxide will be left upon the porcelain. 

430. Copper Oxides and Hydroxides. — Cuprous oxide 
(copper suboxide, red oxide of copper, ruby copper, Cu 2 0) 
is found native and is prepared artificially. It is used 
in coloring glass. Cupric oxide (copper monoxide, black 
oxide of copper, CuO) may be prepared by heating the 
metal in a current of air, or by igniting the hydroxide, 
carbonate, or nitrate. It is used in coloring glass green. 
Two other oxides, tetra-cuprie monoxide (Cu 4 0) and 
copper dioxide (cupric peroxide, Cu0 2 ), are also known. 
There are two hydroxides, the cuprous (CuOH) and the 
cupric [Cu(OH) 2 ]. 

Copper Salts. 

Experiment 299. — Powder some blue vitriol and heat it upon a 
piece of porcelain; as it loses its water, the light blue powder will 
turn white. A drop of water upon the anhydrous powder will restore 
the color. 

431. Some Copper Salts. — Copper nitrate [Cu(N0 3 ) 2 ] 
is prepared by treating copper with nitric acid and evapo- 
rating the solution. On crystallizing from its solution, 
it absorbs three molecules of water (CuN 2 6 , 3H 2 0). It 



372 THE EIGHTH GBODP. 

is easily decomposable and, therefore, has strong oxidizing 
properties. Copper sulphate (CuS0 4 ) is formed by dis- 
solving copper in hot sulphuric acid or the oxide in dilute 
sulphuric acid. It is also prepared from the ores and, 
as a secondary product, in silver refining. It is generally 
found as hydrated crystals (CuS0 4 , 5H 2 0) known as blue 
vitriol, which is largely used in the arts. The color of 
blue vitriol depends upon the presence of its water of 
crystallization. Two native carbonates, malachite and 
azurite, have been mentioned. Some varieties of mala- 
chite are susceptible of a high polish and are highly 
prized for jewels and other ornamental articles. Copper 
acetate is called verdigris, although the term is sometimes 
used to designate the green carbonate that forms on the 
exposure of copper to moist air. Paris green is a copper 
arsenite. It is used in green paints and as an insecticide. 

Note. — The soluble copper salts are active poisons. Such salts 
are formed in copper cooking utensils that are not kept bright. Acid 
solutions (e.g., vinegar) form poisonous compounds with brass or 
copper ntensils even when they are kept perfectly clean. Some per- 
sons prefer to pickle cucumbers in brass or copper kettles because 
they take a more brilliant color. This added color is due to the 
formation of a, poisonous copper compound with the green chlorophyll 
of the pickle. 

EXERCISES. 

1. Read the following equation by unit volumes: 

CH 4 + 20 2 = CO, + 2H 2 0. 

2. Write the equations for the following reactions: (a) Copper 
and nitric acid yield copper nitrate, nitric oxide, and water. (//) Mer- 
cury and sulphuric acid yield mercuric sulphate, sulphurous anhy- 
dride, and water. 

3. The combustion of 1 liter of marsh-gas requires what volume 
of oxygen ? 



THE SILVER FAMILY. 373 

<4. What volume of CH, is reeded to yield 1 cu. m. of steam in 
its combustion? 

5. How many cubic centimeters of S0 2 (at 20° and 740 mm.) can 
be obtained by the action of copper upon 20 grams of H 2 S0 4 ? 

6. Give the symbol and the name of a substance the vapor-density 
of which is 30, and the percentage composition of which is as follows : 
C, 40 ; H, 6.67 ; O, 53.33. 

7. Compare the cost of making HX0 3 from KiT0 3 and from 
NaN0 3 when the cost of KN0 3 is 44 cents per kilogram, that of 
NaN0 3 is 33 cents per kilogram, and that of H 2 S0 4 is 11 cents per 
kilogram. 

8. Required the volume of gases in an eudiometer after the ex- 
plosion of 50 cu. cm. of hydrogen with 75 cu. cm. of oxygen at 150° 
and 760 mm. 

9. Red oxide of copper contains 88.8 parts -of copper and 11.2 
parts of oxygen by weight. Black oxide of copper contains 79.87 of 
copper and 20.13 of oxygen. The formula for the black oxide is 
CuO ; what is the formula for the red oxide ? 

10. How many pounds of copper can be manufactured from a ton 
of pure chalcopyrite (CuFeS.,) ? 

11. When a current of H 2 S is passed through a solution of a cer- 
tain salt, copper sulphide (Cu"S) is precipitated with the formation 
of H 2 S0 4 . AVrite the reaction. 

12. You are given iSTaCl and H 2 S0 4 and required to fill a jar with 
HC1. Describe the process and sketch the apparatus you would use. 

13. What is the difference between liquid ammonia and ammonia- 
water ? 

14. What is the weight of the oxygen contained in 10 grams of 
pure potassium chlorate ? 

15. Compute the percentage composition of common alcohol. 

16. What is the percentage composition of lampblack? 

II. THE SILVER FAMILY. 
Silver: symbol, Ag ; density, 10.5 ; atomic weight, 107.6 ; valence, 1. 

432. Source. — Silver is a widely diffused and somewhat 
abundant element and has been known from the earliest 
times. It is found native, sometimes in masses weighing 



374 THE EIGHTH GROUP. 

several hundred pounds and often alloyed with copper, 
mercury, and gold. It more commonly is found as a sul- 
phide, mixed with other metallic sulphides. Its most 
abundant source is argentiferous galena, although the 
carbonates have been found in richly paying quantities, 
especially in the Leadville (Colorado) mining region. 

433. Preparation. — The processes of preparing metallic 
silver from its ores are numerous and widely different, 
depending largely, in any given case, upon the nature of 
the ore, the position of the mine, the price of labor and 
fuel, etc. It is most commonly obtained by smelting the 
silver ore with lead or copper ore and subsequently sepa- 
rating the silver from the lead or copper. 

434. Properties. — Silver is a beautiful, brilliant white 
metal, harder than gold, softer than copper, exceedingly 
malleable and ductile, and the best-known conductor of 
heat and electricity. It melts at 1040°. The metal is 
unaltered in the air and resists the action of hydrochloric 
acid and cold sulphuric acid, but dissolves readily in nitric 
acid. 

(a) Silver is so malleable that it may be formed into leaves so thin 
that 4000 measure only 1 mm. in thickness; so ductile that 1 gram 
of it may make 1800 meters of wire; and so tenacions that a wire 
2 mm. thick will sustain a weight of more than 80 kilograms. 

(h) Silver unites slowly with the halogen elements and more 
readily with sulphur and phosphorus. The tarnishing of silver is 
generally due to the formation of a silver sulphide by the action of 
hydrogen sulphide present in the atmosphere. 

435. Uses. — Owing to its susceptibility of high polish, 
its permanency and other properties, silver is much used 
for jewelry, plate, and coin. Owing to its softness, it is 



THE SILVER FAMILY. 375 

generally hardened with copper. American and French 
coin contain ten per cent and English coin seven and a 
half per cent of copper. This latter alloy is known as 
"sterling silver," and is most commonly used for silver 
utensils. In some of the states, the mark is protected by 
law. The alloy is also used for chemical utensils as it 
is not acted upon by the fused hydroxides of the alkali 
metals as glass and platinum are. 

436. Oxides. — There are three oxides of silver : silver 
tetrant-oxide (Ag 4 0), silver oxide (Ag 2 0), and silver 
peroxide or dioxide (Ag 2 2 ). When silver oxide (Ag 2 0) 
is digested with ammonia, it forms a very explosive black 
powder, known as fulminating silver. 

Silver Haloids. 

Experiment 300. — Fill three test-tubes one-third full of water and 
pour into each a few drops of a strong solution of AgNC>3. Add 2 or 
3 cu. cm. of a solution of common salt to the contents of the first 
tube and shake it vigorously. Silver chloride will be precipitated 
as a dense, white curdy mass. Add 2 or 3 cu. cm. of a solution of 
potassium bromide to the contents of the second tube and shake 
as before ; a yellowish precipitate of silver bromide will be thrown 
down. Add 1 or 2 cu. cm. of a solution of potassium iodide to the 
contents of the third tube and shake as before ; yellowish, flocculent 
silver iodide will be formed. 

Experiment 301. — Try to dissolve one-third of each of these pre- 
cipitates separately in nitric acid. They will not thus dissolve. 

Experiment 302. — Treat a second third of each precipitate with 
ammonia-water. Determine which dissolves most easily and which 
least easily. 

Experiment 303. — Treat the remainder of each precipitate with a 
strong solution of sodium thiosulphate (§ 403, a). Each of the halo- 
gen salts is "quickly dissolved. 



376 THE EIGHTH GROUP. 

Experiment 304. — Precipitate more silver chloride from a solution 
of silver nitrate by hydrochloric acid or a solution of sodium chloride. 
Filter the solution and wash the precipitate retained upon the filter 
thoroughly with water. Open the filter, spread the curdy silver 
chloride evenly over it, and expose it to the direct rays of the sun. 
The white precipitate quickly changes to violet, the color deepening 
with continued exposure. 

Note. — The last five experiments illustrate the principal processes 
of photography. 

437. The Silver Haloid Compounds. — Silver chloride 
(AgCl) is found native in semitransparent masses, called 
horn silver. It may be prepared by precipitation from a 
solution of any silver salt by a solution of hydrochloric 
acid or of any other chloride. It is insoluble in water 
and acids but easily soluble in ammonia-water. Silver 
iodide or bromide is precipitated from a similar solution 
by a solution of an iodide or bromide. These compounds 
are much used in photography. 

438. Photography. — When silver chloride, bromide, or 
iodide has been exposed to the light, it is more easily 
reduced to the metal than before such exposure. This 
fact, discovered by Niepce and Daguerre, is the founda- 
tion of all photographic processes using silver salts. The 
process of Daguerre consisted in converting the surface 
of a polished silver plate into silver iodide by exposing 
it to iodine vapor. This surface, after exposure to light 
in the camera, was developed and fixed by exposure to 
mercury vapor which converted into the metal so much 
of the silver iodide as had been acted upon by the light. 

In a later process the silver salts were dissolved in 
collodion or gelatin and then coated on glass or on a 



THE SILVER FAMILY. 377 

celluloid film. When such plates are exposed to light 
in the camera, and then immersed in a reducing bath 
or "developer," an image of black, finely divided silver 
appears where the light had touched the plate. In order 
that the remaining silver salt may not become black by 
exposure to light, it is dissolved out and washed away 
by a solution of sodium hyposulphite, which readily dis- 
solves the chloride or iodide of silver, but is without 
effect upon the image of metallic silver. This is the 
function of the " fixing " bath. By this series of opera- 
tions, the photographic negative is produced, with dark 
areas where the light in the camera touched the plate. 
The photographic positive (i.e., the photograph) is made 
by placing a similarly prepared paper below the negative, 
exposing it to light transmitted by the negative, and 
developing it as above described. The silver of the 
image thus formed on the paper is replaced by gold or 
platinum in the "toning" bath, because the resulting 
picture is more permanent and of a more pleasing 
color. 

439. Silver Sulphide and Cyanide. — Silver sulphide 
(Ag 2 S) is an important silver ore and is formed artificially 
by the action of sulphur or hydrogen sulphide upon the 
metal. Silver cyanide (AgCN) is a white curdy precipi- 
tate, insoluble in dilute nitric acid but soluble in ammonia- 
water or in solutions of the cyanides of the alkali or 
alkaline earth metals. It is used in electroplating. 

(a) When a silver spoon is left for a time in an egg or in mustard, 
it becomes blackened by the formation of silver sulphide. Hence 
silver egg-spoons are often gilded. 



378 THE EIGHTH GKOUP. 

Silver Nitrate. 

Experiment 305. — Dissolve a small silver coin in a mixture of 
about 20 cu. cm. of concentrated nitric acid and 20 cu. cm. of water. 

3Ag + 4HNO s = 3AgNO s + NO + H 2 0. 

The silver nitrate thus formed is dissolved in the blue solution, from 
which disagreeable reddish fumes seem to escape into the air. 

Experiment 306. — To separate the silver nitrate formed in the last 
experiment from the copper salt that was formed at the same time, 
dilute the solution to about 300 cu. cm. Add a solution of sodium 
chloride, a little at a time, until no further precipitate is produced 
after the settling of the solution and the addition of more salt. 

AgNO s + NaCl = AgCl + NaN0 3 . 

If too much NaCl is added, part of the precipitated silver chloride 
will be redissolved and lost. Filter out the silver chloride, and wash 
it with hot water until it is free from a soluble chloride. Dry the 
precipitate, separate it from the paper, and gently heat it in a porce- 
lain crucible with a flame until it fuses. Cover the fused silver 
chloride with a piece of sheet zinc, so that the two come into as close 
contact as possible. Add about 10 cu. cm. of dilute sulphuric acid, 
and let the materials stand for a day or two. The zinc will replace 
the silver, forming a solution of zinc chloride. 

2AgCl + Zn = 2Ag + ZnCLp 

Separate the silver from the residual zinc, wash it with dilute sul- 
phuric acid, and then with water until it is clean. Heat a small por- 
tion of the silver on a piece of charcoal and in a blowpipe flame until 
it fuses to a bead. Dissolve this pure silver in dilute nitric acid and 
evaporate the solution to dryness on a water-bath. Dissolve in dis- 
tilled water as much of this pure silver nitrate as is needed, making a 
solution of about 1 part of the nitrate to 20 parts of water. 

440. Silver Nitrate. — Silver nitrate (AgN0 3 ) is pre- 
pared on a large scale by dissolving silver in dilute nitric 
acid and evaporating to crystallization. It is found in 
commerce in crystals. When fused and cast into sticks, it 
is called lunar caustic. In this form it is used in surgery, 



THE SILVER FAMILY. 379 

acting as a powerful cautery. Pure silver nitrate is not 
altered by exposure to sunlight, but when in contact with 
organic substances it blackens, forming insoluble com- 
pounds of great stability. It is consequently used in 
making indelible inks and hair dyes. It is also used in 
medicine and in photography. Like all of the other solu- 
ble silver salts, it is poisonous. 

441. Other Silver Salts. — Silver sulphate (Ag 2 S0 4 ), 
silver phosphate (Ag 3 P0 4 ), and silver carbonate (Ag 2 C0 3 ) 
are among the many important silver salts. 

442. Other Members of this Family. — Ruthenium, pal- 
ladium, and rhodium are rare metals that closely resemble 
each other. They occur in platinum ores and palladium 
is found native. The melting-point of palladium is about 
that of wrought iron ; rhodium is melted with more diffi- 
culty than is platinum ; ruthenium is still less easily 
fusible. Palladium possesses the power of absorbing 
hydrogen in a greater degree than any other metal, one 
volume of the former taking up 600 volumes of the latter 
and forming an alloy with the composition Pd 2 H, one of 
the foundations of the theory that hydrogen is a metallic 
element. 

EXERCISES. 

1. Why do silver coins become blackened when carried in the 
pocket with common sulphur matches? 

2. How much lead may be obtained from 561 kilograms of lead 
sulphide ? 

3. At a very high temperature, Ag 2 may be decomposed much 
as the HgO was in Experiment 29. Write the reaction in molecular 
symbols. 

4. What action have the alkalis upon silver ? 



380 THE EiGHTH GROUP. 

5. If recently precipitated and moist AgCl is placed upon a sheet 
of zinc, a dark color will soon appear at the edge of the salt. 'J 1 he 
chloride will soon be converted into a dark gray powder of finely 
divided silver. Explain. 

6. The change mentioned in Exercise 5 will be much more rapid 
if the AgCl is moistened with HC1. Why? 

7. When silver chloride is fused with an alkaline hydroxide, the 
chloride is reduced to a metal, a non-combustible gas is set free, and 
an alkaline chloride is formed. What is the gas? 

8. If a silver dime is dissolved in HN0 3 , the solution will be blue. 
A solution of AgNOo is colorless. Whence the blue color ? 

9. I want liters of oxygen. What weight of KCIO3 

, T .0896" x 16 

must I use r 

10. (a) How many cubic centimeters of hydrogen may be obtained 
from 1 liter of ammonia? (b) Of nitrogen? (c) How T may the ele- 
mentary gases be obtained from the compound? (d) How may the 
eudiometer be used to free the nitrogen from the hydrogen ? 

11. If HC1 is used instead of cream of tartar with HXaCOs, what 
residue will remain in the biscuit? 

12. (a) Read the equation : 2Ag , 3 P04 + 3H 2 S=2H 3 P04 + 3Ag 2 S. 
(6) Read the equation : Ag 4 P 2 7 + 2 H 2 S = H4P2O7 + 2 Ag 2 S. 
(c) Read the equation : 2AgP0 3 + H 2 S = 2HP0 3 + Ag 2 S. 

1.3. Considering the silver salts symbolized in Exercise 12 to be in 
aqueous solution, summarize the teaching of these three reactions 
with reference to the formation of phosphoric acids. 

14. Write in complete molecules the equation representing the 
reaction to which is due the red fumes noticed in Experiment 73. 

15. How many grams of silver may be prepared from 1000 grams 
of silver chloride ? 

III. THE PLATINUM FAMILY. 

Platinum : symbol, Pt ; density, 21.5 ; atomic weight, 193.3 ; 
valence, 2, 4. 

443. Occurrence, etc. — Platinum is found only in the 
native state, but very seldom pure. The so-called " plati- 
num ore " is an alloy with ruthenium, palladium, rhodium, 



THE PLATINUM FAMILY. 



381 



osmium, iridium, iron, copper, etc. It is found in the 
Ural Mountains, in Brazil, Borneo, California, Alaska, 
and a few other places. It is treated with strong aqua 
regia, and the platinum chloride thus 
obtained is precipitated by means of 
ammonium chloride. The ammonium- 
platinum chloride is then decomposed 
by intense heat, metallic platinum re- 
maining as a residue. The preparation 
of pure platinum is a matter of great 
difficulty. For fusing the metal on the 
large scale, a crucible made of two pieces 
of lime is used with a compound blow- 
pipe. The lime of the crucible success- Fig. iol 
fully resists the high temperature produced, and absorbs 
the slags formed during the operation. 




Properties of Platinum. 

Experiment 307. — Boil 0.5 of a gram of platinum in small frag- 
ments in 10 cu. cm. of aqua regia as long as the metal seems to be 
acted upon. Pour the liquid into an evaporating dish, add aqua 
regia to the remaining platinum and proceed as before, continuing 
thus until all of the platinum has been dissolved. Evaporate the 
solution to dryness upon the water -bath. Dissolve this residue 
(PtCl 4 ) in water. 

Experiment 308. — Heat a few drops of the solution of PtCl 4 in a 

test-tube. Notice the odor of the gas evolved. Hold a strip of 

moistened litmus-paper at the mouth of the test-tube. It will be 

bleached. ^„ „, „ ._, 

2PtCl 4 = Pt 2 + 4C1 2 . 

Experiment 309. — Pour a teaspoonful of a solution of ammonium 
chloride into a test-tube, acidulate it with hydrochloric acid, and to 
it add a drop of the solution of the PtCl 4 just prepared. A yel- 
low powder (2NH 4 Cl,PtCl 4 ) will soon be precipitated. Repeat the 



382 THE EIGHTH GROUP. 

experiment, taking enough of the solutions to make half a tea- 
spoonful of the yellow precipitate, being careful that at last there 
shall be a slight excess of free NH 4 C1 rather than of PtCl 4 in the 
overlying liquid. Allow the precipitate to settle, separate it from 
the clear liquor by decantation, and partly dry it at a gentle heat. 
When the precipitate has acquired the consistence of slightly 
moistened earth, transfer it to a cup-shaped piece of platinum 
foil and heat it to redness in the gas-flame until fumes of NH 4 C1 
are no longer driven off. A gray, loosely coherent, sponge-like 
mass of metallic platinum will remain in the cup ; it is platinum 
sponge. 

Experiment 310. — Make a support for a piece of platinum sponge 
the size of a pea by winding a fine wire spirally into the form of a 
little cup. Heat the sponge to redness in the lamp, and when cold 
hold it 2 or 3 cm. above a small jet of dry hydrogen. The cold gas 
will soon heat the cold sponge to redness ; the sponge will in turn 
ignite the gas. In repeating the experiment, the preliminary heat- 
ing of the sponge, probably, will not be necessary. 

Note. — The heating of the sponge drives off traces of certain 
absorbable gases, such as ammonia, which interfere with the inflam- 
ing power of the platinum. This property of platinum has been 
explained by saying that the metal condenses or even liquefies a film 
of hydrogen and one of oxygen on its surface, and that the two ele- 

nments, when brought together under circumstances 
of such intimate contact, chemically unite at the 
ordinary temperature. 
Experiment 311. — Fill a spirit-lamp with a 
mixture of alcohol and ether. Suspend a spiral 
of platinum wire over the wick and light the lamp. 
When the wire is red-hot, blow out the flame. 
The mixed vapors rising from the wick are oxi- 
dized by the heated platinum ; the spiral is thus 
kept brightly incandescent. This is Davy's glow- 
Fig. 105. lamp. 

444. Properties. — Platinum is a heavy, soft metal of 
tin-white color. It is infusible at the highest temperature 
of the blast-furnace, but yields before the oxyhydrogen 




THE PLATINUM FAMILY. 383 

flame. Its melting-point has been estimated at 2000°. 
It is very malleable, and so ductile that it may be drawn 
into a wire less than 0.001 of a millimeter in diameter. 
Like gold, it has little affinity for the other elements. 
It is not oxidized by oxygen, water, nitric or sulphuric 
acid at any temperature. It dissolves in aqua regia 
more slowly than gold does. It also dissolves in 
chlorine water. Like iron, it may be welded at a white 
heat. It has two oxides, the monoxide (PtO), and the 
dioxide (Pt0 2 ) ; it has two chlorides, the dichloride 
(PtCl 2 ), and the tetrachloride (PtCl 4 ). 

(a) Red-hot platinum absorbs 3.8 volumes of hydrogen, which 
it gives off when heated in a vacuum, the surface of the platinum 
becoming then covered with bubbles. Similarly, hydrogen is absorbed 
by platinum, at the negative electrode in the electrolysis of water, * 
the occluded hydrogen being given off when the current is reversed. 
Oxygen is not absorbed by platinum, but it is condensed on a clean 
surface of the metal. 

(b) Platinum-black is a form of metallic platinum, even more 
finely divided than platinum sponge. It is a soft, dull, black powder. 
It can absorb more than 800 times its volume of oxygen. When 
boiled in water and dried in a vacuum over sulphuric acid, it 
absorbs oxygen from the air so rapidly that the mass becomes red- 
hot. If upon the powder, when cooled after such absorption of oxy- 
gen, some alcohol or ether is dropped, the oxidation of the liquids 
will heat the metal red-hot. 

445. Uses. — On account of its infusibility and its 
chemical inertness, platinum is invaluable to the chemist. 
In the laboratory it is used for crucibles, evaporating 
dishes, stills, tubes, spatulas, forceps, wire, blowpipe tips, 
etc. In sulphuric acid manufacture, large platinum stills 
and siphons are used for concentrating the acid. As its 
rate of expansion is nearly equal to that of glass, it is 



384 THE EIGHTH GROUP. 

used in the manufacture of eudiometers, Geissler tubes, 
incandescent electric lamps, etc. 

(a) On account of platinum forming easily fusible alloys, care 
should be had not to heat platinum utensils with an easily fusible 
metal, e.g., lead, bismuth, tin, or antimony, or any easily reducible 
compound of a metal. They should not be used for fusion with niter, 
the alkalis, or the alkaline cyanides. They should not be heated in 
contact with phosphorus or arsenic nor brought into direct contact 
with burning charcoal. 

(h) " Without platinum it would be impossible, in many cases, to 
make the analysis of a mineral. The mineral must be dissolved. 
Vessels of glass and all non-metallic substances are destroyed by the 
means we used for that purpose. Crucibles of gold and silver would 
melt at high temperatures. But platinum is cheaper than gold, 
harder and more durable than silver, infusible at all temperatures 
of our furnaces and is left intact by acids and alkaline carbonates. 
Platinum unites all the valuable properties of gold and of porcelain, 
resisting the action of heat and of almost all chemical agents. With- 
out platinum the composition of most minerals would have yet re- 
mained unknown." — Liebig. 

446. Osmium and Iridium. — These rare metals are 
found in "platinum ore," as already stated. They are 
of extreme infusibility. Osmium is the heaviest known 
substance, it having a density of about 22.48. Its alloy 
with iridium (osmiridium) is used for tipping gold pens 
as it is not attacked by acids, and for the bearings of the 
mariner's compass as it does not oxidize and is non- 
magnetic. Iridium has a density of about 22.38. It has 
a white luster resembling that of polished steel. An 
alloy of one part of iridium and nine parts of platinum 
is extremely hard, as elastic as steel, more difficultly 
fusible than platinum, unalterable in air, and susceptible 
of a beautiful polish. This alloy was adopted by an inter- 
national commission for the standard metric measures. 



THE PLATINUM FAMILY. 385 

EXERCISES. 

1. Sulphuric acid is poured upon niter; name the two substances 
that you obtain. Write the reaction. 

2. Why is moist calico more easily bleached with chlorine than 
is dry calico ? 

3. From 8 kilograms of potassium nitrate, how much nitric acid 
can be liberated ? How much sulphuric acid will be required ? 

1. Write the formulas for selenic acid and for tellurious acid. 

5. Complete the following equations : 

XaCl+H 2 S0 4 = HC1 + 

NaCl + H 2 S0 4 = 2HC1 + Xa 2 S0 4 

6. Write the name and full graphic formula for 

S-(S0 2 )-(HO) 
S-(S0 2 )-(HO) 

7. If sulphuryl chloride is poured into water, we have the follow- 
ing reaction : SO2CI2 + 2H 2 = H 2 S0 4 + 2HC1. How much dry HC1 
may be thus prepared from 135 grams of S0 2 C1 2 ? 

8. If a factory uses daily 100 tons of coal that contains 2 per cent 
of sulphur, assuming that all the sulphur is converted to sulphuric 
acid, what weight of sulphuric acid will the products of combustion 
contain during 300 days' run? 

9. Write the reactions expressing the preparation of at least 
5H 2 S0 4 , using not more than two molecules of nitric acid. 

10. Which is the more easily fusible, platinum or calcium 
oxide ? 

11. What is the difference between ammonia and ammonium ? 

12. How many grams of silver chloride may be prepared from 
1000 grams of American coin silver? 

13. Write the names and formulas for the salts formed by the 
union of potassium hydroxide with each of the following acids : sul- 
phurous, sulphuric, nitrous, nitric, chlorous, and chloric. 

11. Write the names and the formulas for the salts formed by the 
union of calcium hydroxide and each of the acids mentioned in the 
preceding exercise. 

SCHOOL CHEMISTRY — 25 



386 THE EIGHTH GROUP. 

Gold: symbol, Au ; density, 19.265; atomic weight, 195.7; 
valence, 1, 3. 

447. Occurrence. — Gold is widely distributed in nature, 
but in only a few places is it found in quantities sufficient 
to repay the cost of obtaining it. It is generally found 
in the native state alloyed with silver. Native gold is 
found in the quartz veins that intersect metamorphic 
rocks and in the alluvial deposits, called placers, formed 
by the disintegration of gold-bearing rocks. 

(a) The richest deposits of gold are in California, Colorado, Ne- 
vada, Alaska, Siberia, South Africa, and Australia. Native gold is 
found in crystals, nuggets, grains, and scales. While the particles 
are sometimes so small as to be invisible in even "paying" quartz, 
a single nugget, weighing 184 pounds and valued at £837(3, 10s. 6rf., 
was found in Australia. Gold compounds are also found in nature. 

448. Preparation. — In quartz-mining the ore is first 
pulverized. The gold is then extracted from the pow- 
dered mineral by means of mercury. The gold amal- 
gam thus formed is subjected to distillation. In " placer 
digging " the lighter constituents of the alluvial deposit 
are washed away, the heavier gold remaining in the 
"wash-pan" or "cradle." In "hydraulic mining" im- 
mense streams of water are directed, under great pres- 
sure, against the surface of the auriferous deposit. In 
this way great quantities of sand, clay, and gravel are 
disintegrated and hurried forward in a turbid torrent, 
from which the heavy gold particles settle into inter- 
stices previously prepared in the sluices through which 
the muddy mass is caused to flow. Much of the gold 
now mined is contained in sulphide ores which must be 
roasted befure the gold can be recovered. The gold 



THE PLATINUM FAMILY. 387 

of such roasted ores is commonly made soluble by treat- 
ment with potassium cyanide or by chlorine. The solu- 
tion is then washed out with water. The gold is 
precipitated from the potassium cyanide solution by 
zinc, and from the chloride by ferrous sulphate. 

Properties of Gold. 

Experiment 312. — Add a few drops of a strong solution of auric 
chloride (AUCI3) to a liter of water. Into this dilute solution drop 
one or two pieces of phosphorus the size of a mustard seed, and place 
the whole in the sunlight. In the course of a few hours the water 
will have a distinct purplish tint. This will deepen in color until 
finally, if the solution has the proper strength, a beautiful ruby-red 
liquid will be obtained. The color of this liquid is due to finely 
divided metallic gold. 

449. Properties. — Gold is a brilliant, beautiful, orange- 
yellow metal. It is the most malleable and ductile of 
the metals. It may be beaten into leaves not more than 
0.0001 of a millimeter thick; one gram of it may be 
drawn into 3240 meters of wire. It is softer than silver 
and nearly as soft as lead. It fuses at 1063.5° and 
volatilizes at very high temperatures. It is not attacked 
by oxygen or water at any temperature. It does not 
dissolve in any simple acid except selenic, but dissolves 
readily in aqua regia or in any other acid liquid that 
evolves chlorine. 

(a) One ounce of gold-leaf may be made to cover 189 square feet, 
while 280,000 leaves placed one upon another measure only one inch 
in thickness. One grain of gold will gild two miles of fine silver 
wire. Ordinary gold-leaf transmits green light. Gold may be pre- 
cipitated in so fine a state that it remains suspended in the liquid, 
causing it to appear ruby-red by reflected light or blue by transmitted 
light. The red color of ruby glass is due to the presence of gold in a 
finely divided state. Gold is sometimes called the " king of metals." 



388 THE EIGHTH GROUP. 

450. Uses. — Gold is used for coinage, jewels, gilding, 
and other purposes, for which it is well adapted by its 
beautiful color and luster, its unalterability and com- 
parative rarity. Pure gold is so soft that coins and jew- 
els made of it would soon wear out. It is, therefore, 
hardened by alloying with copper. American and 
French gold coins contain one-tenth copper ; British 
gold coins, one-twelfth. 

(a) The purity of gold in jewels is estimated in carats, pare gold 
being "21 carats fine." An alloy containing two-thirds gold is "16 
carats fine." 

(b) The compounds of gold are of little chemical interest. There 
are two oxides, the monoxide (aurous oxide, A112O) and the tri oxide 
(auric oxide, gold sesquioxide (AiioO,?). There are two chlorides, 
AuCl and A11CI3. Aurous cyanide (AuCX) dissolved in a solution 
of potassium cyanide is used in electrogilding. 

EXERCISES. 

1. What takes place when sodium is thrown into water? 

2. Describe an experiment showing the difference between a mix- 
ture and a compound. 

3. State the effect of heat upon Mn0 2 , KCIO3, yH 4 Cl, XII4XO3, 
phosphorus, and sulphur respectively. 

4. You are given Zn, H 2 S0 4 , KIIO, and H 2 0, and required to pre- 
pare hydrogen from them by two distinct processes. Describe the 
processes and write the reaction for each. 

5. I have two cylindrical jars of hydrogen, one of which I hold 
mouth upward, the other mouth downward. At the end of 30 seconds, 
I plunge a lighted taper into each jar. Tell what you would expect 
to take place in each case. 

6. What are the products of the combustion of hydrogen sulphide 
in the air? 

7. How can you make II0SO4 from sulphur, water, and nitric add? 

8. What elements can be obtained from IIC1, NH 3 , and H 2 0? 
How would you obtain them in each case? 

9. (a) When hydrogen is burned in air, what is Die product? 
('/) When it is burned in chlorine? 



THE PLATINUM FAMILY. 389 

10. An electric spark is produced in a mixture of 120 cu. cm. of 
hydrogen and 60 cu. cm. of oxygen. How would you conduct the 
experiment so as to show the gaseous condensation ? 

11. You are required to prepare oxygen from chlorine and water. 
How would you do it ? 

12. You are given some mercury in a glass flask, a lamp, and some 
glass tubing, and required to make pure oxygen. How will you do 
it under ordinary barometric conditions? 

13. When nitric acid is poured on copper, how does the action differ 
from a simple solution ? 

II. You are given ammonium carbonate and nitric acid and re- 
quired to prepare laughing-gas from the materials. How will you 
doit? 

15. What is the fineness of British gold coin in carats? 

16. (a) Where is sulphur found ? (Jj) How is hydrogen sulphide 
made, and what are its properties? (c) What is meant by oxidizing 
agents and what by reducing agents ? 

17. When a thin stream of sulphuric acid flows into a retort filled 
with broken bricks heated to redness, the following reaction takes 
P lace : H 2 S0 4 = S0 2 + H 2 +C 

(a) "What weight and (b) what volume of oxygen can be thus pre- 
pared from 50 grams of H0SO4, C.P. ? 

18. Write the formulas for potassium sulphite, potassium-hydrogen 
sulphite, calcium sulphite, and calcium-hydrogen sulphite. 

19. Write the name and a full graphic formula for 

S-(S0 2 )-(HO) 

s I 
%S— (S0 2 )— (HO) 

20. Write the graphic formula for phosphorus tetriodide (P2T4) 
indicating trivalent phosphorus. 

21. Write the graphic formula for pvrophosphoric chloride (CI4P2 
3 ). 

22. (a) Write the graphic formula for H3PO3. (ft) Does this 
formula indicate a dibasic or a tribasic acid ? 

23. Explain the fact that when new flannel is first washed in an 
alkaline soap, it becomes yellow. 

24. (a) How would you distinguish between platinum and silver ? 

(b) Between platinum and tin? (c) Between silver and tin? (d) 
Between gold and "fool's gold"? 



APPENDIX. 



1. The Chemical Elements. — An alphabetical list of the elements 
with their symbols and atomic weights is given below. In the body 
of the book, some of the atomic weights were given in approximate 
numbers, for greater ease in memorizing and computation. In the 
table below, the atomic weights are given according to the latest 
report of the American committee on atomic weights. (See third 
page of cover.) 

Atomic Atomic 



Name. 


Symbol. 


Weight. 


Name. 


Symbol. 


Weight. 


Actinium . 






Indium . 


. In . . 


. 113.1 


Aluminum . 


1 Al .' ! 


26.9 


Iodine 


.1 . . 


. 125.89 


Antimony . 


. Sb . . 


119.5 


Iridium . 


. Ir . . 


. 191.7 


Argon . . 


. Ar . . 


40.? 


Iron . . 


. Fe . . 


. 55.5 


Arsenic . 


. As . . 


74.45 


Krypton . 


. Kr . . 


. 59.? 


Barium . . . 


. Ba . . 


136.4 


Lanthanum 


. La . . 


. 137.6 


Beryllium . 


. Be . . 


9.0 


Lead . . 


. Pb . . 


. 205.86 


Bismuth 


. Bi . . 


206.5 


Lithium . 


. Li . . 


. 6.97 


Boron . . 


. B . . 


10.9 


Magnesium 


. Mg . . 


. 24.1 


Bromine 


. Br . . 


. 79.84 


Manganese 


. Mn . . 


. 54.6 


Cadmium . 


. Cd . . 


111.55 


Mercury . 


• Hg . . 


. 198.5 


Caesium 


. Cs . . 


131.9 


Molybdenun 


l . Mo . . 


. 95.3 


Calcium 


. Ca . . 


39.8 


Neodymium 


. Nd . . 


. 142.5 


Carbon . . 


. C . . 


11.9 


Neon 


. Ne . . 


. 20.? 


Cerium . . 


. Ce . . 


138.0 


Nickel 


. Ni . . 


. 58.25 


Chlorine 


. CI . . 


35.18 


Niobium 


See Colnmbium 


Chromium . 


. Cr .. . 


51.7 


Nitrogen 


. N . . 


. 13.93 


Cobalt . . 


. Co . . 


58.55 


Osmium 


. Os . . 


. 189.6 


Colnmbium 


. Cb . . 


93 


Oxygen . 


.0 . . 


. 15.88 


Copper . . 


. Cu . . 


63.1 


Palladium 


. Pd . . 


. 106.2 


Crypton 


See Krypton 




Phosphorus 


. P . . 


. 30.75 


Erbium . . 


. E . . 


164.7 


Platinum " 


. Pt . . 


. 193.4 


Ethereon ? 






Polonium 






Fluorine 


. F '. . 


18.9 


Potassium 


'. K . . 


! 38.82 


Gadolinium 


. Gd . . 


155.8 


Praseodymiu 


m Pr . . 


. 139.4 


Gallium . 


. Ga . . 


69.5 


Radium . 


. Ra . . 


.225.? 


Germanium 


. Ge . . 


71.9 


Rhodium 


. Rh . . 


. 102.2 


Glucinum 


See Berylliiu 


i 


Rubidium 


. Rb . . 


. 84.75 


Gold . . . 


. An . . 


195.7 


Ruthenium 


. Ru . . 


. 100.9 


Helium . 


. He . . ' 


4.? 


Samarium 


. Sm . . 


. 149.2 


Hydrogen . 


. H . . 


1.0 


Scandium 


. Sc . . 


. 43.8 



390 



APPENDIX. 



391 







Atomic 






Atomic 


Name. 


Symbol. 


W EIGHT. 


Name. 


Symbol. 


Weight. 


Selenium 


. . Se . 


. . 78.6 


Thulium . 


. Tm . . 


169.4 


Silicon 


. . Si . 


. 28.2 


Tin . . . 


. Sn . . 


118.1 


Silver 


• • Ag . 


. 107.11 


Titanium 


. Ti . . 


47.8 


Sodium . 


. Na . 


. 22.88 


Tungsten 


. W . . 


182.6 


Strontium 


. . Sr . 


. 86.95 


Uranium . . 


. U . . 


237.8 


Sulphur . 


. S . 


. 31.83 


Vanadium . 


. V . . 


51.0 


Tantalum 


. Ta . 


. 181.5 


Xenon . . 


. X . . 


128.? 


Tellurium 


. Te . 


. 126.5 


Ytterbium . 


. Yb . . 


171.9 


Terbium . 


. Tr . 


. 158.8 


Yttrium . . 


. Y . . 


88.3 


Thallium 


. Tl . 


. 202.61 


Zinc . . . 


. Zn . . 


64.9 


Thorium . 


. Th . 


. 230.8 


Zirconium . 


. Zr . . 


89.7 



2. Weighing. — The laboratory should be provided with at least 
two balances, one of the platform type for the heavier weighings, 
and one of the scale-pan 
type sensitive to 0.0 1 of 
a gram. A really good 
balance is a delicate piece 
of apparatus and requires 
careful use and preserva- 
tion. Substances that 
corrode metal (iodine for 
example) should not be 
allowed to come into con- 
tact with the scale-pans, and all metallic parts of the balance should 
be protected from corrosion by acid fumes, etc. With the object to 

be weighed on one side of the bal- 
ance and an exact counterpoise on 
the other, count up the total weight 





from the vacant places in the box of weights (Fig. 108) and then 
verify the result by another count as the weights are returned to 



392 



APPENDIX. 



their proper places in the box. The process looks simple, but accurate 
weighing requires technical skill. 



3. Metric Measures. — Chemists of all countries use the inter- 
national or metric units almost exclusively. The decimeter rule is 
shown as being divided into 10 centimeters, each 
of which is divided into 10 millimeters. The cubic 
decimeter measures a volume called a liter (pro- 
nounced teeter). The cubic centimeter (cu. cm.) 
is 0.001 of a liter (1.). The weight of 1 cu. cm. of 
water at the temperature 4° is a gram (g.). These 
three units, the liter, the cubic centimeter, and the 
gram, are the ones of most frequent occurrence in 
chemical works. The actual weights and meas- 
ures should be habitually used in every school 
laboratory. 



Fig. 100. 



4. Thermometers. — Chemists use the centigrade 
thermometer almost exclusively. One or more 
centigrade thermometers (chemical), hav- 
ing the scale marked on the glass tube, and 
having no frame like that of the ordinary 
house thermometer, should be in every 
school laboratory. Straight glass tubes, of 
uniform diameter, with cylindrical instead 
of spherical bulbs, are preferable j such 
instruments can be passed tightly through 
a cork, and are free from many liabilities 
to error to which thermometers with paper 
or metal scales are always exposed. A 
cheaper kind of thermometer, having a 
paper scale inclosed in a glass envelope, 
will answer for many experiments. 

Fig. 110. 



5. Glass-working. — Much of the chem- 
ist's apparatus is made of glass which softens and becomes plastic 
when heated. Skillful workers in wood or metal may be found in 
almost any town, but glass-working will generally devolve upon the 
teacher and pupil. It is, therefore, discussed at some length in 
this place. 



APPENDIX. 393 

(a) Glass Tubing. — Glass tubes bent into various shapes are con- 
stantly needed. The pupil should acquire dexterity in preparing 
these for himself. Glass tubing is of two qualities, hard and soft. 
The former softens with difficulty and is desirable only for ignition- 
or combustion-tubes. But little of it will be needed. It is generally 

better to buy the ignition-tubes required. Soft 

glass tubing will be needed in larger quantities. 

In purchasing, it is recommended that the greater 

Fig. 111. p ar £ b e f a s i n g] e s i ze . Figure 111 shows desirable 

sizes and the proper thickness of the glass for each size. By using, 

habitually, one size of tubing, the various articles made therefrom 

are more easily interchangeable than they would otherwise be. 

(b) Cutting and Bending Tabes. — Glass tubing and rods must gen- 
erally be cut the desired length. For this purpose, lay the tube or 
rod upon the table and make 
a scratch at the required dis- 
tance from one end with a 
three-cornered file. Hold the 
tubing in both hands, as shown 
in Fig. 112, with the scratch 
away from you and the two 
thumbs opposite the mark. 
With a sharp motion, push out the thumbs and pull back the fingers. 
The glass will snap squarely off at the desired place. The best flame 
for bending ordinary tubes is that of a fish-tail gas-burner, but that 
of a spirit-lamp will do. Be sure that the tube is dry; do not breathe 
into it before heating it. Bring the part of the tube where the bend 
is desired into the hot air above the flame ; when it is thoroughly 
warm, bring it into the flame itself. Heat about an inch of the tube, 
holding it with both hands and turning it constantly that it may be 
heated uniformly on all sides. The tube should be held between the 
thumb and first two fingers of each hand, the hands being below the 
tube, palms upward and the lamp between the hands. The desired 
yielding condition of the glass will be detected by feeling better than 
by seeing, i.e., the fingers will detect the yielding of the glass before 
the eye notices any change of color or form. When the glass yields 
easily, remove it from the flame and gently bend the ends from you. 
If the concave side of the glass is too hot, it will "buckle"; if the 
convex side is too hot, the curve will be flattened and its channel 
contracted. Practice, and practice only, will enable you to bend a 




Fig. 112. 



394 



APPENDIX. 




tube neatly. When a tube or rod is to be bent or drawn near its 
end, a temporary handle may be attached to it by softening the end 

of the tube or rod, and press- 
ing against the soft glass a 
fragment of glass tube which 
will adhere strongly to the 
softened end. This handle 
may subsequently be removed 
by a slight blow or by the 
aid of a file. If a consider- 
able bend is to be made, so 
that the angle between the 
arms will be very small or 
nothing, as in a siphon, the 
curvature can not be well 
produced at one place in the 
tube, but should be made by 
heating, progressively, several 
centimeters of the tube, and bending continuously from one end of 
the heated portion to the other (Fig. 114). The several parts of such 
a bent tube should all lie in the same plane so that the 
finished tube may lie flat on a level surface. It is difficult 
to bend tubing large enough for U-tubes which would 
better be bought. When the end of a tube or rod is to be 
heated, it is best to begin heating the glass about 2 cm. 
from the end, as cracks start easily from an edge. Smooth 
the sharp edges at the ends of the tube by slight fusion 
in a flame. Anneal the bent tube by withdrawing it very 
gradually from the flame so as not to let it cool suddenly. fig. 114. 
Never lay a hot tube on the bench, but put it on some 
poor conductor of heat until it is cool. Asbestos board or paper is 
convenient for this purpose. Gradual heating and gradual cooling 
are alike necessary. Glass tubing may be advantageously united by 
rubber tubing when the substance to be conducted will not corrode 
the latter, or when the temperature employed is not too high. Short 
pieces of rubber tubing are much used as connectors to make flexible 
joints in apparatus. Gas delivery-tubes, etc., are. generally made in 
several pieces joined by rubber tubing connectors, which, by their 
flexibility, add much to the durability of the apparatus. Long ulass 
tubes bent several times and connecting heavier pieces of apparatus 



(P 



APPENDIX. 395 

are almost sure to break, even with careful use. The internal diam- 
eter of the connector should be a little less than the external diameter 
of the glass tubing. The connection may be made more easily by 
wetting the glass. 

(c) Drawing Tubes. — In order to draw a glass tube down to a finer 
bore, thoroughly soften it on all sides uniformly for 1 or 2 cm. of its 
length and then, taking the glass from the flame, pull the parts 
asunder by a cautious movement of the hands. The length and 
fineness of the drawn-out tube will depend upon the length of tube 
heated and the rapidity of motion of the hands. If the drawn-out 
part of the tube is to have thicker walls in proportion to its bore 

c. 



Fig. 115. 

than the original tube, keep the heated portion soft for two or three 
minutes before drawing out the tube, pressing the parts slightly 
together the while. By this process the glass will be thickened at 
the hot ring. By cutting the neck at a, with a file, jets are formed. 
(d) Closing Tubes. — Take a piece of tubing long enough to make 
two closed tubes of the desired length. Heat a narrow ring at the 
middle of the tube and draw it out slightly. Direct the point of 
the flame upon the point c (Fig. 115) which is to become the bottom 
of one tube, draw out the heated part and melt it off. Each half of 
the original tube is now closed at one end, 
but they are of different forms. You can 
not close both ends satisfactorily at the 116, 

same time. A superfluous knob of glass generally remains upon the 
end. If small, it may be removed by heating the whole end of the 
tube, and blowing moderately into the open end. The knob being 
hotter than any other part, yields to the pressure from wiinin and 
disappears. If the knob is large, it may be drawn off by sticking to 
it a fragment of tube, and then softening the glass above the junction. 
The same process may be applied to the too-pointed end of the right- 
hand half of the original tube, or to any bit of tube that is too short 
to make two closed tubes. When the closed end of: a tube is too 
thin, it may be strengthened by keeping the whole end at a red heat 
for two or three minutes, turning the tube constantly between the 
fingers. In all of these processes keep the tube in constant rotation 



396 APPENDIX. 

that it may be heated on all sides alike. It will be difficult for the 
pupil satisfactorily to work tubing large enough for test-tubes. They 
would better be bought. They come in nests of assorted sizes. 

(e) Blowing Bulbs. — This is a more delicate operation than any 
yet described. It requires considerable practice to secure even mod- 
erate success. It is better, as a general thing, to buy funnel-tubes 
and bulb-tubes than to make them. 

CO Welding Glass Tubes. — The well-fitted ends of two pieces of 
glass tubing may be joined by heating them to redness and pressing 
them together while in a plastic condition. Practice is necessary to 
good results, but the skill should be acquired as funnel-tubes and 
other pieces of apparatus often need mending. If necessary, the end 
of one tube may be enlarged by rapidly turning the glass in the flame 
until it is highly heated, and then, while it is still in the flame, flaring 
it outward with an iron rod. Hold the ends together and heat them 
well with a pointed flame, until they are united all around. Force 
air in at one end to swell out the joint a little, heat it again until 
the swelling sinks in, blow it out again, and repeat the process until 
the joint is smooth and the pieces well fused into each other. With- 
out this repeated heating and blowing, the joint is likely to crack open 
when cooled. 

(g) Piercing Tubes. — A hole may be made in the side of a tube 
or other thin glass apparatus by directing a pointed blowpipe flame 
upon the glass until a spot is red-hot, closing the other end, if open, 
with the finger and blowing forcibly into the. open end. The glass is 
blown out at the heated spot. The edge may be strengthened by 
laying on a thread of glass around it, and fusing the thread to the 
tube in the blowpipe flame. 

(Ji) Glass-cutting and Cracking, etc. — For cutting glass plates a 
glazier's diamond is desirable, but efficient and cheap " glass-cutters," 
made of hardened steel, may be bought. For shaping broken flasks, 
retorts, and other pieces of thin glassware, cracking is more satisfac- 
tory. A scratch is made with a file, preferably at the edge of the 
glass. Apply a pointed piece of glowing charcoal, a fine-pointed 
flame or a heated glass or metal rod to this scratch. The sudden 
expansion by heat will generally produce a crack. If the heat does 
not make one, touch the hot spot with a wet stick. A crack thus 
started may be led in any desired direction by keeping the heated 
rod or fine flame moving slowly a few millimeters in front of it as it 
advances. 



APPENDIX. 



397 




A flask or retort neck may sometimes be cracked round by tying a 
string soaked in alcohol or turpentine round the place, setting fire 'to 
the string and keeping the flask turning. When the string has burned 
out, invert the flask and plunge it into water up to the heated circle. 
It will generally crack as desired. 

The lower ends of glass funnels and the ends of gas delivery-tubes 
that enter the generating bottle or flask should be ground off obliquely 
on a wet grindstone, or shaped thus with a 
file wet with a solution of camphor in tur- 
pentine, to facilitate the dropping of liquids 
from such extremities. With a little care 
and patience, a hole may be drilled through 
glass by using a file kept wet with the solu- 
tion mentioned. Such a hole may easily 
be enlarged or given any desired shape with 
a file thus wet. 

The lips of bottles may be ground flat 
by rubbing them on a flat surface sprinkled 
with emery-powder kept wet. The bottle should be grasped by the 
neck and rubbed around with a gyratory motion, pains being taken 
to prevent a rocking motion whereby first one side of the lip is ground 
and then another, thus leaving the bottle in as bad a condition at the 
end of the work as at the beginning. The work may be finished by 
rubbing with fine emery-powder on a piece of plate or 
window-glass until all parts of the ground surface lie in 
the same plane. 

6. Pipettes and Graduates. — Tubes drawn out to a 
small opening at one end and used to remove 
a small quantity of a liquid from a vessel 
without disturbing the bulk of its contents, 
are called pipettes. They often carry a bulb 
or cylindrical enlargement. The manner of 
using them is shown in Fig. 118. They are 
often graduated. A cylindrical measuring- 
glass, graduated to cubic centimeters (Fig. 
119), is almost indispensable in the labo- 
ratory. 

7. Woulffe Bottles. — A very convenient substitute for 
Woulffe bottles may be made by perforating the glass Fig. 119. 




Fig. 118. 




398 



APPENDIX. 




cover of a fruit jar, as already described. The holes carry cork or 
rubber stoppers through which the several tubes pass, as shown 
in Fig. 120. 

8. Thin-bottomed Glassware. — Glass vessels 
are largely used for heating liquids in the lab- 
oratory. Such vessels should have uniformly 
thin bottoms that they may not be broken by 
unequal expansion when heated. If moisture 
from the atmosphere or other source accumulates 
on the outer surface, it should be carefully wiped 
off before or during the heating. 

Retorts are often used. Those that have 
tubulures (Fig. 35, s) are preferable to those that 
have not. 

Florence flasks are much used instead of 
retorts, as they cost much less. They may be 
bought in any size desired and with their bot- 
toms rounded or flattened. Heated retorts and 
flasks should not be placed on the table, as the 
sudden cooling may break them. They may 
better be placed on rings covered with listing or made of straw or 
other poor conductor of heat. 

Beakers are thin, flat-bottomed glasses w r ith slightly flaring rims. 
They are convenient for heating liquids when it is desirable to reach 
every part of the vessel, as with a stirring-rod. They are generally 
sold in nests of different sizes. Beakers of more than a liter's capac- 
ity are too fragile to be desirable. 

Test-tubes are thin glass cylinders, closed at one end and having 
lips slightly flared. The mouth should be of such a size that it may 
be closed by the ball of the thumb. 
A test-tube rack should be made 
or bought, to hold the tubes up- 
right when in use and to hold them 
inverted when not in use. 

Test-tubes may be held in an 
inverted position, as at the pneu- 
matic trough or water-pan, by 
weighting them with lead rings cut with a saw from lead pipe. The 
ring should be of such a size that it will easily slip over the tube, but 
not over the lip of the tube. Test-tubes may be easily cleaned with 




APPENDIX. 



399 




Fig. 122. 



little cylindrical brushes made of bristles held between twisted wires. 
They cost but a few cents each. The chief danger in cleaning a test- 
tube is that the bottom may be broken out. The brush should there- 
fore have a tuft of bristles at its end. When the upper end of a tube 
is held in the fingers during the heating, the tube should be rolled or 
turned in the flame so that all sides may be equally heated. 

9. Filtering. — Funnels that have an angle of exactly 60° should be 
chosen. The circular piece of filter-paper should be folded first on 
its diameter, then again at right angles to the 
first fold, and then opened out so as to leave 
three folds on one side and one on the other. 
It is then to be placed in a funnel, the funnel 
placed in proper position, and the liquid to 
be filtered carefully poured upon the paper. 
If the first filtration does not clear the liquid, 
the filtrate should be poured back upon the 
same filter for refiltration. Observation and 
experiment will show other good ways of 

folding the filter-paper for the funnel. 

For coarse and rapid filtering, the neck of the 
funnel may be plugged with tow or cotton. For 
filtering solutions that would destroy the texture 
of the filter-paper, a plug of asbestos or of gun- 
cotton is placed in the neck of the funnel. 

The funnel may be supported in any convenient 
way. Sometimes it may be placed in the neck of 
the bottle, care being had that it does not fit air- 
tight (see Fig. 57). It may often be supported from the retort-stand 
or other independent support. When convenient, the lower end of 
the funnel should touch the side of the vessel that 
receives the filtrate, so that the latter may fall quietly 
rather than in splashing drops. The end of the 
funnel neck should be ground off obliquely, as shown 
in Fig. 117. 

When a precipitate has been collected upon a filter, 
it may be washed by filling the filter two or three 
times with distilled water and allowing it to run 
through. A washing-bottle is of great convenience, 
the stream of water being driven out at c by air from 
the lungs forced in at a. The stream of water is Fig. 124. 




Fig. 123. 




400 APPENDIX. 

directed so as to wash the precipitate from the sides of the filter 
toward its apex. The jet may be carried by a piece of flexible tubing 
attached to c, so that it may be turned in any direction without 
moving the bottle. When a precipitate is very heavy, it may be 
washed by shaking it up with successive quantities of water in a test- 
tube, and pouring oft* the water when the precipitate has settled down. 
A wet glass rod held against the lip of the test-tube greatly assists in 
pouring off the liquid withont disturbing the precipitate. 

10. Corks, etc. — It is not always easy to obtain corks of good qual- 
ity and considerable size. Many experiments have failed through 
defects in the corks used. Use bottles with small mouths when you 
can. Choose corks cut across the grain rather than those cut with 
the grain, as the latter often provide continuous channels for the 
escape of gases. Select those that are as fine grained as you can get. 
They will generally need to be softened before use. This may be 
done by rolling on the floor with the foot, on the table with a board, 
or with a cork-squeezer made for that purpose. Corks may be made 
less porous by holding them for a few minutes under the surface of 
melted paraffin wax. 

In boring holes through corks, a small knife-blade or rat-tail file 
may be used, but a set of brass cylinders made for the purpose is 
more convenient. Such a set of cork borers and the way of using 
them are shown in Fig. 125. Use a borer with a diameter a little 




Fig. 125. 



less than that of the glass tubing to be used. "When the borer be- 
comes dull, grind or file the outer beveled edge and, with a sharp 
knife-blade, pare off the rough metal on the inside of the edge. 

Rubber stoppers are more durable than cork and much to be pre- 
ferred. They may be bored as above described. If they harden, they 
may be softened by being kept for a time in a closed flask containing 



APPENDIX. 401 

a few drops of turpentine. If the glass tube enters the bored stopper 
with much difficulty, wet the outside of the tube with turpentine. 

In passing glass tubes through stoppers of cork or rubber, see 
that the end of the tube is smooth, hold the tube as near as possible 
to the stopper, and force it in with a slow, steady, rotary, onward 
motion. Do not hold a funnel-tube by the funnel, or a bent tube 
at the bend, if you can avoid doing so. If the glass tube enters 
the bored cork with much difficulty, smear the outside of the tube 
with soap and water. Test all joints made in the manner described 
in § 22. 

The sticking of glass stoppers is a frequent source of trouble in the 
laboratory. Many methods of loosening them have been suggested. 
When one fails, another must be tried. Under such circumstances, 
patience and persistence are recommended. It is hardly ever neces- 
sary to break the bottle. Generally, the stopper may be started by 
tapping it lightly on opposite sides alternately with a block of soft 
wood. The expansion of the bottle neck by heat will often loosen the 
stopper. The heat may be applied by friction with the fingers or a 
piece of tape, by a flame, or by hot water. If the application of heat 
is continued too long, the stopper as well as the neck will expand, and 
the trial end in failure. As a last resort, fit two pieces of soft wood 
between the lip of the bottle and the lower side of the projecting part 
of the stopper. Tie them firmly in place and soak in water for sev- 
eral hours. If the wood does not swell enough to start the stopper, 
pour hot water over the wooden pieces, and the trouble will generally 
be at an end. 

When you pour a liquid from a bottle, as into a test-tube, hold the 
bottle in the right hand with the label toward the palm. Remove 
the stopper with the little finger or with the third and fourth fingers 
of the left hand, the thumb and forefinger of which may hold the 
test-tube. Remove the liquid drop that adheres to the lip of the 
bottle by touching it with the stopper, replace the stopper, and 
return the bottle to its proper place. It is seldom necessary to place 
either stopper or bottle on the table. In a little while you will 
acquire the habit of doing these things in this way and thus avoid 
much annoyance. 

11. Stands, Supports, Baths, etc. — Flasks, etc.. are often supported 
over the lamp by a retort-stand, as shown in Figs. 32 and 35. This 
stand has a heavy base and several movable iron rings of graduated 

SCHOOL CHEMISTRY 26 



402 



APPENDIX. 



sizes secured to the vertical rod by binding screws. Glass vessels thus 
supported are well protected from the direct flame of the lamp by a 
piece of wire-gauze, as shown in Fig. 32. Occasionally a very grad- 
ual and even heating is desired. Under such circumstances, the 
wire-gauze may be replaced by a sand-bath, which consists of a shal- 
low pan, beaten out of sheet-iron and filled 
with sand. Sometimes it is desirable to 
heat a vessel moderately, keeping it con- 
tinuously below a certain temperature. 
This may be accomplished by placing the 
vessel in another vessel, partly filled with 
water, and heating the water, as shown in 
Fig. 71. Copper cups with tops made of 
concentric rings that may be adapted to 
the size of the vessel are offered for sale. 
A good enough water-bath may be made 
of an old tinned fruit-can. Care should 
be had that the water of the bath is no't 
allowed to boil away. Figure 1*26 shows 
various clamps and fittings for a retort- 
stand, by means of which tubes, flasks, 
retorts, etc., are easily held in any desired 
position. Many convenient supports may 
be made with corks and glass rods stuck 
on inverted funnels. A convenient sup- 
port for a small vessel may be made in the 
form of an equilateral triangle by twisting 
together three pieces of soft-iron wire at the corners, as shown in 
Fig. 127. Each of the wires may be run through the stem of an 
ordinary clay pipe. The support may be placed upon the ring of a 
retort-stand, or held by a cork into which the 
twisted wires at one corner have been thrust. A 
convenient support for test-tubes, etc., may be 
made by binding the middle part of a copper wire, 
1 or 2 millimeters in diameter, about a stout cork. 
The free ends of the easily flexible wire may be 
wound spirally around the test-tube. The cork 
serves as a handle ; if perforated, it may be placed 
upon the rod of the retort-stand. The wire may be bent so as to place 
the tube in any desired position. 




Fig. 126. 




APPENDIX. 



403 




Fig. 128. 



12. Mortars. — A mortar is a vessel, m, in which solid substances 
may be powdered with a pestle, i. They are made of iron, porcelain, 
agate, etc. Porcelain mortars of the best quality are 
made of "Wedgwood"; they are imglazed, should 
not be suddenly heated, and may be cleaned by rub- 
bing them with sand wet with nitric acid, or sul- 
phuric acid, or caustic potash, or soda, according to 
the nature of the substance to be removed. Agate 
mortars are very small and expensive. In many 
cases a stout bowl will answer as a mortar, while a pestle may be 
made of hard wood. Many substances may be powdered on a hard 
surface by the use of a rolling-pin, like that used by a pastry cook, or 
by rolling a stout bottle over them. If a solid is to be broken by 
blows preparatory to powdering, an irou mortar and pestle are desir- 
able. The pestle may be worked through 
a hole in a pasteboard cover, which will 
prevent fragments of the solid from flying 
out of the mortar. Often it is better to 
wrap the solid in a paper or a cloth, and 
then to break it with blows of a hammer. 
In using a mortar for pulverizing, it is 
better to put only a small quantity of 
the substance into the mortar at once, 
sifting it frequently, and returning the 
coarser j>articles to the mortar for further 
trituration. The sifting may be done 
by rubbing the powder lightly with the ringer upon a piece of muslin 
tightly stretched over the mouth of a beaker. 




Fig. 129. 



13. The Pneumatic Trough. — For collecting gases over w r ater, the 
pneumatic trough, in some form, is indispensable. A convenient 
trough is shown in Fig. 7, and described in § 21. The pan, /, may 
be of earthenware, while a flower-pot saucer will answer for e. Two 
flat blocks of any material heavier than water may be used, instead of 
the saucer, for the support of the inverted gas receiver, g. With this 
apparatus the receiver must be filled outside of the trough. The 
mouth being closed with the hand, a flat piece of wood, glass, or card- 
board, the bottle may be quickly inverted and placed in position so 
that its mouth is closed by the water in /. If any air gets into g 
during this operation, the work must be done again. While one 



404 



APPENDIX. 



bottle is filling with gas, another is to be made ready. When filled 
with gas, the first bottle may be removed from the trough by slipping 
a shallow plate or saucer beneath its mouth and removing plate and 
bottle together. Enough water will be retained in the plate to seal 
the mouth of the bottle. If the lip of the bottle has been ground 
flat, a piece of window-glass will answer instead of the plate. As 
successive bottles are filled, the trough may become inconveniently 
full of water, some of which may be dipped out or removed with a 
rubber-tube siphon. 

Any bucket or tub with a hanging shelf having holes bored in it, 
will make an efficient pneumatic trough. 

When it can be secured, a pneumatic trough similar to that shown 
in Fig. 100 is desirable. It may be made of boards carefully joined 
c and painted, but is preferably 
lined with sheet-lead. It should 
be sunk in a table and provided 
with a water-cock and a drain- 
pipe. Gas receivers are easily 
filled with water in the well, win, 
and placed upon the shelf, b, 
which is to be below the water 
level. The dimensions of mn are 
to be determined by the size of 
the largest vessels that are to be sunk in it, and the size of b by the 
size and number of gas receivers that are likely to be in use at any 
one time. Grooves may be provided in the shelf, ft, running parallel 
to the side, ac. These grooves allow the rubber deliveiw-tube to pass 
under the edges of the receivers without compression. In lifting 
large receivers from the well of a small trough, the water level may 
,be brought below the shelf, b. Under such circumstances, more water 
may be introduced from a pail or by the water-cock, or a jug of water 
previously placed within convenient reach may be placed in the well 
and subsequently removed when the filling of the receiver with gas 
raises the level of the water too high. 

Porcelain pneumatic troughs for use with mercury may be bought 
for a little money of any dealer in chemical wares, but a cheap sub- 
stitute may be made by cutting, or by burning with a blowpipe flame 
or with a red-hot iron, a depression in a block of hard wood. The 
principal dimension of the trough thus made should be horizontal, 
the bottom being rounded so that it will conform to the outline of a 




Fig. 130. 



APPENDIX. 405 

test-tube or of a cylinder placed in it. Its depth should be a little 
more than the diameter of the test-tube or cylinder used. 

In collecting gases over water, two difficulties must be guarded 
against. First, if from any cause the tension of the gas within the 
apparatus becomes less than the atmospheric pressure, water from 
the pneumatic trough may be forced back through the delivery-tube 
into the generating-flask. Cold water being thus suddenly admitted 
to a hot flask, the latter is broken and sometimes a more serious ex- 
plosion takes place. This danger is especially present in thus collect- 
ing a gas somewhat soluble in water. In stopping the evolution of 
a gas, remove the delivery-tube from the trough, and remove the 
adhering water-drops before removing the lamp. Whenever the 
delivery of a gas begins to slacken, watch the delivery-tube ; if water 
begins to " suck back " toward the flask, quickly remove the delivery- 
tube from the water, or, still better, break a rubber connection or 
loosen the stopper of the generating-flask. When a liquid is used 
in the flask, this danger of " sucking back " may be avoided by the 
use of a safety-tube, as shown at s, Fig. 29. In case a partial vacuum 
should be formed in the flask, b, atmospheric pressure would force 
down the liquid in the lower part of the tube, s, and thus admit air 
instead of raising the liquid in c to the greater height necessary to 
allow it to enter b. 

The second difficulty to be guarded against is the production of 
too great a pressure within the apparatus by allowing any part of 
the delivery-tube to dip too far beneath the surface of the water in 
the trough. Owing to the high density of the liquid used, this diffi- 
culty is especially present in the collection of gases over mercury. 
The pressure thus produced may develop leaks in the apparatus or, 
in certain cases, force the liquid of a flask out through the funnel- or 
safety-tube. 

14. Gas-holders. — It is often convenient to have a supply of 
oxygen, hydrogen, and other gases on hand. Gas-holders are con- 
venient for storing such gases for use. One form of easy construction 
is shown in Fig. 131. It consists of an outer vessel, a, open at the 
top, and an inner vessel, 6, open at the bottom. Both may well be 
made of galvanized iron ; a may be a barrel, cask, or earthen crock. 
The upper end of b is hammered into saucer-shape so that its highest 
point shall be at the middle. At this highest point is inserted a gas- 
cock, having its free end smooth and slightly tapering, for the recej> 



406 



APPENDIX. 




tion of rubber tubing. Three hooks or eyes are attached to the edge 

of the upper end of b, from which extend cords that are knotted 

together at the lower end of the supporting cord, c. The cord, c, may 
pass over pulleys in a frame, as shown in the 
figure, or over pulleys supported from the ceiling, 
the frame being omitted. Fill a with water. 
Open the stop-cock, remove the weights from c, 
and allow b to sink into a. Be sure that there is 
enough water in a to cover the highest point of b. 
Connect the stop-cock, by rubber tubing, with 
the gas generator, but not until all air has been 
expelled from the tubing. Open the stop-cock 
and place weights at the free end of c. By 
making these weights heavier than b the pressure 
in the generating apparatus may be reduced as 
far as desired. As gas is delivered, b will rise. 
The apparatus is shown on a larger scale at G, 
Fig. 69. When the generation of gas has ceased, 
or when b is full, close the stop-cock, remove the 
G> tubing, and leave suspended from c only enough 

weights to counterbalance b. For most schools, a 6- or 8-gallon crock 

(preferably tall and narrow) w T ill be large enough for the outer vessel. 

The stop-cock may be had of any plumber or gas fitter; any tinsmith 

can make the vessel, b. 

When gas is wanted from the holder, connect the gas-cock of b with 

the apparatus to be used, open the cock, remove weights from c and, 

if necessary to produce the desired 

pressure, place them upon b. It 

is customary to paint the oxygen 

holder red and the hydrogen holder 

black for purposes of ready distinc- 
tion. 

A convenient gas-holder may be 

made from a large glass bottle or 

a jug by passing two glass tubes 

through the cork, providing one 

with a piece of rubber tubing and 

the other with a stop- or pinch-cock. 

The bottle being filled with water, the gas-generator is connected 

with the stop-cock which is then quickly opened. As the gas enters 




APPENDIX. 407 

g through a, water escapes through the siphou, c. The pressure on 
the generator at starting may be relieved by sucking at c to start the 
action of the siphon. Gas is delivered from g through a, by connect- 
ing c with a supply of water elevated on a shelf (siphon delivery, if 
desired) or with any other supply of water under moderate pressure. 
When a gas is to be kept for only a short time, a rubber gas-bag is 
a convenient substitute for a gas-holder. It is easily portable and 
has other advantages. One may be bought for two or three dollars. 

15. Lamps. — In laboratories, where illuminating-gas is provided, 
the most convenient form of lamp for heating purposes is the Bunsen 
burner, which gives a very hot and 
smokeless flame. A fair substitute 
for a Bunsen burner may be made by 
inverting a wide-necked glass funnel 
over any ordinary gas-burner, sup- 
porting it in any convenient way so 
that air may have free passage between 
the sides of the burner and the glass 
as shown in Fig. 133. The funnel is 
to be put into position before the gas 
is lighted. The gas supply is to be Fig. 
controlled so as to produce a smokeless flame. 

When a very small flame is used with the Bunsen burner, the flame 
may drop down into the tube. This may be prevented by laying a 
small piece of wire-gauze over the top of the tube and pressing its 
edges down against the sides of the tube before lighting the gas. 

If the laboratory is not supplied with gas, an alcohol-lamp may be 
used. The Berzelius or Argand lamp burns alcohol, and is convenient 
for many purposes where much heat is necessary, e.g., the preparation 
of oxygen in considerable quantity. Lamps made especially for burn- 
ing gasoline vapor, and provided with a variety of burners, may be 
bought. The vertical pipe that supports the gasoline supply may be 
utilized for retort-stand purposes. Gasoline is cheaper than alcohol. 
Special heating apparatus is made in great variety. 

16. Blowpipes. — Bunsen blast-lamps, hot-blast blowpipes, etc., are 
provided in great variety for use with a blower (Fig. 134). Mouth 
blowpipes, one form of which is shown in Fig. 135, may be bought in 
a great variety of forms. In using the mouth blowpipe, air should be 
forced through it by the action of the cheeks rather than by the action 




408 



APPENDIX. 




Fig. 135. 



of the lungs. A little practice will enable teacher or pupil to main- 
tain a continuous current of air from the nozzle of the blowpipe, 

breathing naturally in the mean- 
time. When this air current is 
directed against a lamp- or a gas- 
flame, the appearance of the flame 
varies according to the strength of 
the blast and the position of the 
jet relative to the flame. When 
the tip of the blowpipe is held in the 
flame and a strong blast is forced 
through it, we have a well-defined 
cone of blue flame beyond or out- 
side of which is an outer and more 

*IG. 154. „„. . . 

luminous cone. I his is the oxi- 
dizing flame. Oxidation takes place most rapidly at the point of 
the outer cone or just beyond it. 
But if the tip of the blow- 
pipe is held just outside the 
flame and the blast is gentle, 
the flame is less changed in its general character, the greater part of 
it consisting of intensely heated carbonaceous vapors ready to take 
up oxygen. This is the reducing flame. The substance to be reduced 
is held in the large, luminous cone and thus out of contact with the 
air. Charcoal makes a good support for the substance to be reduced. 

17. Soldering. — It is often very convenient to be able to solder 
together tw T o pieces of metal. A bit of soft solder, the size of a hazel- 
nut, may be had gratis of any good-natured tinsmith or plumber. 
Cut this into bits the size of a grain of wheat. Dissolve a teaspoon- 
ful of zinc chloride in water and bottle it. It may be labeled " sol- 
dering fluid." Having bought or made an alcohol-lamp, you are ready 
for work. For example, suppose you are to solder a bit of wire to a 
piece of tinned ware. If the wire is rusty, scrape or file it clean at 
the place of joining. By pincers or in any convenient way hold the 
wire and tin together. Put a few drops of "soldering fluid " on the 
joint, hold the tin in the flame so that the wire shall be on the upper 
side, place a bit of solder on the joint and hold in position until the 
solder melts. Remove the joint from the flame, holding the tin and 
wire together until the solder has coolec}. The work is done. The 



APPENDIX. 409 

mouth or blast blowpipe, previously mentioned, will be a convenient 
substitute in many cases for the alcohol-lamp. If you have a " sol- 
dering iron " — strange misnomer, for it is made of copper — you can 
do a wider range of work, as many pieces of work can not be held in 
the lamp^flame. 

18. Deflagration-spoon. — A deflagration-spoon for burning phos- 
phorus, sulphur, etc., in oxygen may be bought for a few cents of any 
apparatus dealer. One may be made by soldering the bowl of any 
ordinary metal spoon or any other metal cup to a long wire handle 
and bending the wire upward at a right angle near the cup. A cup 
may be hollowed in the side of a piece of chalk or lime and then 
fastened to a wire handle. If a metal cup is used for combustions in 
oxygen, it is well to line it with some infusible material like clay, 
powdered chalk, lime, or plaster of Paris. A coated cork capsule, 
smaller than the one mentioned in Experiment 53, may be provided 
with a wire handle and used as a deflagration- spoon. In any case, 
the upper part of the wire handle should be straight so that it may 
be thrust through the cover of the jar. 

19. Evaporating Dishes, Crucibles, and Furnaces. — Evaporating 
dishes are generally made of porcelain and provided with a projecting 
lip and glazed on both sides, or only on 
the inside. The latter are the cheaper, 
but the former are the more desirable. 
Sizes from 8 to 15 cm. in diameter are 
best adapted to the needs of most classes. 
They should be supported upon wire 
gauze, the sand- or the water-bath, and G ' 

never exposed to the naked flame. For granulating zinc or fusing 
salt, Hessian and clay crucibles and capsules are cheap, and largely 
used. They will endure a very high temperature, but should be 

heated somewhat gradually. They 
may be heated in a coal or coke 
fire in any ordinary stove. Heated 
crucibles may be handled con- 
veniently with crucible tongs, two 
common forms of which are shown 
Fig. 137. in Fig. 137. 

20. Metal Retorts. — Many gases may be prepared by carefully 
heating the materials in a Florence flask or a glass retort, but an 





410 APPENDIX. 

iron or a copper retort is very desirable. Such retorts may be had 
in a variety of forms, made of iron, sheet-iron, or copper, of dealers 
in chemical or physical apparatus, at prices ranging from one dollar 
upward. The author has made a very cheap and wholly efficient 
retort as follows : Cut a thread on each end of a piece of inch gas- 
pipe, a, 6 or 8 inches long. Screw an iron cap, K, over one end. 
For the other end, provide an iron "reducer," t, carrying a piece of 
f-inch gas-pipe, e, about 15 or 18 inches long. The materials being 
placed in the capped tube, the reducer 
■ with its pipe is screwed on the open 
^t end of the tube. The closed retort 

FlG - 138# may then be thrust into the coals of 

any ordinary stove. A piece of glass tubing may be sealed with 
plaster of Paris into the end of the small iron tube. This affords 
a good means for connecting the retort with rubber tubing, and 
protects the latter from burning. If desirable, the inner surface 
of K may be smeared with wet plaster of Paris before screwing it 
upon a. If, at the end of the experiment, t is not easily removed 
from «, a few blows will generally start it. The parts of this retort 
may be had of any gas- or steam-fitter. 

21. Ventilating Chamber, etc. — A chamber, 50 cm. by 75 cm., or 
larger, with glass sides and provided with a ventilating flue that has 
a good draught is important for experiments with chlorine, hydrogen 
sulphide, etc. The ventilating flue may, in some cases, be advan- 
tageously connected with the chimney. The chamber may be built 
against the chimney and provided with two or three narrow slits 
through the brickwork from top to bottom of the closet. At least 
one side of the chamber should be made so that it may be opened, 
but when shut it should fit closely. Openings that may be closed 
should be made in the bottom of the chamber for the admission of 
air so that a current may be obtained. A lamp burning in the 
chamber will aid in keeping up the current and carrying off the 
offensive gases. 

22. Test Papers, etc. — Litmus-paper, both blue and red, should 
be kept on hand for the detection of acids and alkalis. Litmus 
is a blue coloring matter prepared from certain lichens and found in 
commerce in small cubical masses somewhat soluble in water. White, 
unsized paper is stained with an infusion of 30 grams of litmus in 250 
cu. cm. of boiling water. Such a paper is reddened by an acid. The 



APPENDIX. 411 

blue litmus-paper may be faintly reddened by immersion in vinegar 
or any other dilute acid. This reddeued paper is colored blue by the 
action of an alkali. 

A purple liquid may be prepared by steeping red-cabbage leaves 
in water, and filtering. Such a cabbage solution will be colored red 
by an acid or green by an alkali. 

A ruby-red tincture of cochineal may be prepared by digesting 
3 grains of cochineal in a mixture of 50 cu. cm. of alcohol and 200 
cu. cm. of water at the ordinary temperature for several days. Acids 
will change the color of such a tincture to orange ; alkalis will 
change it to violet carmine. 

Turmeric-paper, prepared by staining unsized paper with a tincture 
(alcoholic solution) of turmeric root (curcuma), is sometimes used as 
a test for alkalis which turn it from yellow to brown. 



INDEX. 



[References are to pages.] 



Acetates . 

Acetic acid 221, 

aldehyde 

Acetylene 

Acid, Acetic 221, 

Benzoic 

Boric 

Bromic . . . „ ... . 

Butyric 

Carbolic 262, 

Carbonic 209, 

Chromic 

Citric 

defined 

Dichromic 

Ferric 

Formic 

Glacial acetic 

Glycolic 

Hydriodic 

Hydrobromic 

Hydrochloric 

Hydrocyanic 

Hydrofluoric 

Hypobromous 

Hyponitrous 

Hyposulphurous . . . 344, 

Iodic 

Lactic 

Malic 

Muriatic 

Nitric 

Nitrosyl-sulphuric .... 

Nitrous 

Nordhausen 

Oleic 

Oxalic , 



Acid Palmitic 254 

Perbromic 119 

Periodic 121 

Phosphoric 298 

Phosphorous 298 

Poly silicic 279 

Propionic 254 

Pyroboric 188 

Pyroligneous 251 

salt 88 

Silicic 278 

Stannic 283 

Stearic 254 

Sulphuric 337 

Sulphurous 337 

Tartaric 257 

Acids, Arsenic 305 

Chlorine . . 114 

Fatty 251, 254 

Hydrocarbon 251 

Nomenclature of . . . 21, 89 

Phosphorus 298 

Tests for 42 

Thionic 345 

Actinium 176 

Agate 277 

Air 55-00 

Albumin 272 

Albuminoids .... 272, 247 

Alcohol 242 

lamp 407 

Alcoholic fermentation . . . 246 

Aldehydes 250 

Alizarin 263 

Alkali defined 87 

Allotropism 46 

Allylene 231 



413 



414 



INDEX. 



Alum 103 

Chrome 316 

Alumina 193 

Aluminum 191 

bronze 193 

hydroxide - . . 193 

oxide 193 

Amalgams 183 

Amethyst 277 

Ammonia 64-70 

Ammonia-water 66 

Ammonium 68, 165 

chloride 165 

nitrate 166 

Analysis 24 

Anhydrides 00 

Anhydrite 173 

Aniline 262 

Animal life .... 59, 216, 218 

Anthracene 262 

Anthracite 198 

Antimoniureted hydrogen . . 309 

Antimony 307 

Apatite 290 

Aqua ammonia (}() 

fortis 77 

regia 115 

Argand lamp 407 

Argol 257 

Argon 62 

Arrow-root 269 

Arsenic 302 

acids 305 

Arsenious acid 305 

Arseniuret 302 

Arsine 303 

Atom 13 

Atomic attraction 14 

symbols 10 

symbols, Table of ... . 390 

theory 120 

weight 127, 131 

weights, Table of .... 390 

Atomicity of molecules . . . 133 

Auric oxide 388 

AvogadroVs law ...... 130 



Azurite 369 

Bacteria, Nitrifying .... 83 

Baking-powders 156 

Baking soda . 155 

Balances, Laboratory . . . 391 

Barite 318 

Barium 175 

Base defined 86 

Bases, Nomenclature of . . . 91 

Basic hydrogen 90 

salt 89 

Basicity of acids 90 

Beakers 398 

Becquerel rays 170 

Beer 245 

Beet sugar 267 

Bell-metal 282 

Benzene 230, 262 

Benzine 231 

Benzoic acid 203 

Beryllium 168 

Berzelius lamp 407 

Bessemer steel 350 

Bicarbonate of potash . . . 102 

of soda 155 

Bichromate of potash . . . 315 

Bismuth 309 

Bismuthyl 310 

Black-ash 153 

Black lead 197 

Blast-furnace 350 

Blasting gelatin 81 

Bleaching 102 

Bleaching-powder 102 

Blende 180,318 

Blowpipe, Compound .... 48 

Blowpipes 407 

Body defined 10 

Bohemian glass 279 

Boiler-scale 52, 174 

Bone-black 199 

Bone-phosphate 173 

Borax 189 

Boric acid 188 

Boron 187 



INDEX. 



415 



Bottle-glass 280 

Brandy 245 

Brass 181, 370 

Braunite 123 

Bread-making 269 

Brimstone 320 

Britannia metal 282 

Bromic acid 119 

Bromine 118 

Bronze 282, 370 

Aluminum 193 

Bubbles .... 30, 31, 48, 49 

Bunsen burners 407 

Butane 225, 229 

Butter 260 

Butterine 261 

Butter of antimony .... 309 

Butyl 226 

Butylene 231 

Butyric acid 254 

Butyrin 260 

Cadmium 182 

Caesium 165 

Cairngorm stone 277 

Calamine 180 

Calcite 168 

Calcium 168 

bicarbonate 172 

carbide 170 

carbonate 172 

chloride 170 

hydrate 171 

hydride 170 

hydroxide 171 

nitride 170 

oxides 163 

phosphate 173 

Calomel 184 

Candle-power 232 

Cane-sugar 266 

Caramel 267 

Carats 388 

Carbohydrates 265 

Carbolic acid ' . . . . 262, 263 

Carbon 196 



Carbon dioxide 42, 209 

disulphide 121, 330 

monoxide 205 

oxides 205-113 

Carbonates 212 

Carbonic acid .... 209, 212 

acid gas 42 

anhydride 209 

Carbonyl 205 

Carboxyl 251 

Carburet 204 

Carnelian 277 

Casein 272 

Casserite 281 

Castor-oil 261 

Catalysis 38 

Caustic lime 171 

potash 163 

Celestine 175 

Celluloid 272 

Cellulose 271 

Cement 280 

Cementation steel 355 

Cerium 275 

Cerusite 287 

Chalcedony . 277 

Chalcocite 318, 369 

Chalk 168 

Charcoal, Animal 199 

Wood 198 

Cheese 272 

Chemical arithmetic .... 136 

changes 12 

equations 137 

Chemism 14, 15 

Chemistry defined 19 

Chloral 250 

hydrate 250 

Chloric acid 114 

Chlorine 97 

acids . 114 

oxides 113 

Chloroform 241 

Chlorous acid . ." . . . . 114 

Chrome alum 316 

iron ore 314 



41G 



Chrome yellow .... 287, 316 

Chromic acid 315 

Chromite 314 

Chromium 314 

Cinnibar 182 

Citric acid 257 

Clay 191, 194, 279 

Coal, Mineral 197 

gas 233 

tar 234, 262 

Cobalt 367 

Cod-liver oil 262 

Coke 234 

Collodion 272 

Columbium 289 

Combining weight 127 

Combustion 43, 58 

Compound radicals . . 225, 226 

Compounds 13, 18, 20 

Conservation of energy and 

mass 17 

Copper 369 

glance 369 

Coral 168 

Corks 400 

Corrosive sublimate .... 185 

Corundum 191, 193 

Crocus 361 

Crown glass 280 

Crucible steel 360 

tongs 409 

Crucibles 409 

Cryolite 116, 191, 194 

" Crystal " 280 

Cupric hydroxide 371 

Cuprite " 369 

Cuprous hydroxide .... 371 
Cyanide, Silver 377 

Iron 364 

Cyanides 214 

Cyanogen 213 

Dragon process 103; 

Decane 225, 229 

Decay ' . 58, 246 

Decyl 226 



Definite proportions, Law of . 76 

Deflagration-spoon .... 409 

Dextrin 261) 

Dextrose 267, 268 

Diamond 196 

Diastase 245 

Dichromic acid 315 

Didymium 316 

Distilled liquors 245 

Dithionic acid 345 

Double salt 88 

Drying oils 261 

Dyad denned 93 

group 168-186 

Dynamite 81 

Earthenware 194 

Element 13 

Elements, list of 390 

nomenclature of .... 20 

Embalming 247 

Emerald 191, 341 

Emery 191, 103 

Endothermic 141 

Energy, Conservation of . . 17 

denned 9 

Epsom salt 179 

Equations 137 

Erbium 175, 155 

Essential oils 261, 262 

Ethane 225, 229 

Ethereon 32 

Ethers . . . .* 248 

Ethine 222 

Ethyl 226 

alcohol 244 

ether 248 

Ethylene 229 

series 222, 229 

Eudiometer 41) 

Evaporating dishes .... 409 
Exothermic 141 

Factors 136 

Families and groups .... 143 

Fats, Common 260 

Fatty acids 251, 254 



417 



Fatty bodies, Natural . . . 258 

Feldspar 191, 194, 279 

Fermentation 246 

Fermented liquors 245 

Ferric acid ....... 364 

hydroxide 362 

salts 362 

Ferrous salts 362 

sulphide 362 

Fertilizers 299 

Fibrin 272 

Filter, Charcoal 202 

Filtering 399 

Fire-damp 228 

Fixed oils 261 

Flames 232 

Flashing-point 223 

Flint 277 

Flint-glass 283 

Florence flasks 398 

Flowers of sulphur .... 320 

Fluorine 116 

Fluor-spar 117 

Food of animals . . . 218, 273 

of plants 217, 299 

Formic acid 251 

aldehyde 250 

Formula, Constitutional . . . 222 

Molecular 20 

Structural 222 

Fruit-sugar 267 

Fulminating silver 375 

Funnels 397 

Fusible metab 311 

Gadolinium 195 

Galena 283, 286 

Galenite ...... 283, 286 

Gallium 147, 194 

Galvanized iron 181 

Garnet 191 

Garnierite 366 

Gas-carbon 234 

Gases, Collection of . . . 27, 29 

Gas-holders 405 

Gay-Lussac law 134 

SCHOOL CHEMISTRY 27 



Gay-Lussac tower 339 

Gelatin 273 

Blasting. 81 

German silver 181 

Germanium 147, 281 

Glacial acetic acid 251 

phosphoric acid 299 

Glass 279 

Soluble 279 

[ stoppers 401 

Glass tubing 393 

| Glass-working 392 

Glauber salt 152, 318 

Glover tower 339 

Glucose 267, 268 

Glycerin 257 

Glycerol 255 

Glycol 255 

Glycolic acid . 256 

Gold 386 

Gold-leaf 387 

Graduates 397 

Gram 392 

Grape sugar 267 

Graphic symbols 94 

Graphite 196, 197, 198 

Gravimetric computations . . 137 

Green vitriol 363 

Groups and families .... 143 

Guncotton 81, 271 

Gunpowder 80 

Gypsum . . . . . 173, 291, 318 

Halogen group 97-126 

Hard soap 259 

water 174 

Hartshorn . 64 

Hausmanite 123 

Heavy spar ..... 175, 318 

Helium 62 

Hematite 348 

Heptad defined 93 

group 97-126, 348 

Heptane 225, 229 

Heptyl 226 

Hexad defined ..„,,. 93 



418 



Hexad group. . . . . .314-347 

Hexane 225, 229 

Hexyl 226 

Homologous series 222 

Hydraulic cement 280 

lime 172 

mining 380 

Hydriodic acid 121 

Hydrobromic acid 119 

Hydrocarbon acids .... 2-31 

series 222 

skeletons 219 

Hydrocarbons 219 

Hydrochloric aci 1 105 

Hydrocyanic acid 214 

Hydrofluoric acid 118 

Hydrogen 24-34 

antimonide 309 

arsenide 303 

Basic 90 

Combustion of 48 

dioxide 53 

monocarbide 227 

persulphide 330 

phosphide 296 

salt 88 

sulphide 324 

Hydroxy 1 53 

Hypobromous acid .... 119 

Hypochlorous acid . . . . 114 

Hyponitrous acid . •. . . . 84 

Hypophosphorous acid . . . 298 

Hyposulphites 345 

Hyposulphurous acid . . 344, 345 

Illuminating oils 223 

Illuminating-gases 232 

Indium 194 

Inulin 269 

Invert-sugar 267 

Iodic acid 121 

Iodine 120 

Iodoform 241 

Iridium 384 

Iron 348-364 

Galvanized 181 



Isomers 220 



Jasper 



277 



Kaolin 149 

Kerosene . ' . 223 

Kisserite 17'.) 

Krypton 62 

Lactic acid ....... 257 

ferment 246 

Lactose 267 

Lampblack 203 

Lamps, Laboratory .... 407 

Lanthanum. 190 

Lard 260 

oil 262 

Laughing-gas 70, 71 

Law of Avogadro 130 

of definite proportions . . 76 

of Gay-Lussac 134 

of multiple proportions . . 76 

The periodic 143-147 

Lead 283 

Red 285 

tree 180 

White 287 

Leblanc process 153 

Levulose 267, 268 

Lichtenberg's metal .... 311 

Life 216-218 

Animal 59 

Lignite 198 

Lime ' 169 

Hydraulic 172 

Slacked 171 

Limestone 168, 172 

Lime-water 171 

Limonite 348 

Linseed oil 2(51 

Liquid oxygen 39, 43 

Liter 392 

Litharge 285 

Lithium 16 1 

Litmus-paper 42,410-, 

Lubricatiug-oils 223 



419 



Luminosity of flames . . . 232 

Lye, Concentrated .... 157 

Potash 162 

Magenta (dye) 263 

Magnesia 179 

alba 179 

Magnesite ■ . . 179 

Magnesium 178, 179 

salts 179 

Magnetite 348 

Malachite 360 

Malic acid 257 

Malleable iron 369 

Malt 245 

Maltose 267 

Manganese 123 

dioxide ........ 35 

oxides 123 

. salts 124 

Maple-sugar 267 

Marble 168, 172 

Marsh-gas 227 

series 222, 225 

Marsh's test 308 

Matter, Changes in . . . 10, 11 

defined 9 

Mechanical changes .... 12 

Mendeleef 144 

Mercury 182 

oxides 184 

salts 184 

Metaarsenic acid 305 

Metal defined 14 

Metallic elements 143 

Metamers 221 

Metaphosphoric acid .... 298 

Methane 225, 227 

Methene 222 

Methyl 226 

alcohol 242 

ether 248 

hydride 227 

Methylene . 229 

Metric measures 392 

Meyer, Lothar 144 



Mica 279 

Minium 285 

Mispickel 302 

Mixed gases 49 

Mixtures 18 

Molasses 266 

Molecular formulas .... 20 

structure 221 

weight 130 

Molecule defined 12 

Molecules, Atomicity of . . . 133 

Molybdenum 316 

Monad defined 93 

group 149-167 

Mordants .362 

Mortar ........ 171, 403 

Mother of vinegar 254 

Multiple proportions, Law of . 76 

Muriatic acid 106 

Muscovado sugar 267 

Naphtha group 223 

Naphthalene 262 

Nascent state 115 

Natural gas 240 

Neat's-foot oil 262 

Neodymium 316 

Neon 62 

Neutralization 87 

Nickel 366 

Niter 163 

Nitrates 82 

Nitric acid 77 

anhydride 75 

oxide 72 

Nitrobenzine 262 

Nitrocellulose 271 

Nitrogen .... 56, 60-63, 289 

acids 77-85 

oxides 70-75 

Nitroglycerin 81 

Nitrosyl 72 

Nitrosyl-sulphuric acid . . . 341 

Nitrous acid 83 

oxide 70 

Nitryl ......... 74 



420 



Nomenclature 20-22 

Nonane 225,229 

Non-metallic elements . . . 143 

Nonyl 22(3 

Nordhausen acid 344 

Normal salt 88 

Octane 225, 229 

Octyl . . 226 

Oil, Illuminating 223 

of bitter almonds .... 263 

of lemon 262 

of turpentine 262 

of vitriol 342 

Oils 261 

Oleriant gas 229 

Olefines ........ 229 

Oleic acid 254 

Olein 258 

Oleomargarine 261 

Olive-oil 262 

Onyx 277 

Opal 279 

Open-hearth steel process . . 357 

Organic chemistry . . . 217, 263 

matter 216 

Orpiment 305 

Orthophosphoric acid ... 298 

Osmiridium 384 

Osmium 384 

Ossein 273 

Oxalic acid 256 

Oxidation 58 

Oxygen 24, 34-47 

Ozone 45 

Palladium 379 

Palmitic acid 254 

Palmitin 258 

Paper 271 

Paraffin oil 223 

Paraffins 225, 226 

Solid 225. 229 

Parchment, Vegetable . . . 271 

Paris green 372 

Pearl-ash 162 



Peat 198 

Pentad defined 93 

group 289-813 

Pentane 220. 229 

Pentathionic acid 345 

Pentyl . 226 

Perbromic acid 119 

Percentage composition . . . 140 

Perchloric acid 114 

Periodic acid 121 

law 14:3-147 

Pestles 403 

Petroleum 222 

Pewter 282 

Phenol 263 

Phosphine 296 

Phosphoric acid 298 

Phosphorite 290 

Phosphorous acid 298 

Phosphorus 15, 289 

acids 208 

Phosphoryl 208 

Phosphureted hydrogen . . 206 

Photography 376 

Physical changes 12 

Pig iron 352 

Pipettes 397 

Pitchblende 176, 316 

Plant food 217, 299 

Plaster of Paris 173 

Plate glass 280 

Platinum 380 

sponge 382 

Platinum-black 383 

Plumbago 1!»7 

Plumbic oxide 285 

Pneumatic trough 403 

Polonium 17(5 

Polymers 221 

Polysilicic acid 27!» 

Porcelain l'.»4 

Portland cement 280 

Potash 102 

Potassium 158 

bicarbonate 162 

bromide 161 



421 



Potassium carbonate . . . . 162 

chlorate 114 

chloride 161 

cyanide 161, 214 

ferricyanide .... 863, 864 
ferrocyanide .... 363, 364 

fluoride 161 

hydrate 163 

hydroxide 163 

iodide 161 

nitrate 163 

Potassium-hydrogen carbonate 162 
Powder, Smokeless .... 81 
Praseodymium .... 289, 316 

Products 186 

Proof-spirit 247 

Propane ...... 223, 229 

Propionic acid 254 

Propyl . . 226 

Propylene 229 

Proteids 273 

Prussian blue 364 

Puddling furnace 354 

Pyrite 318 

Pyroarsenic acid 305 

Pyroboric acid 188 

Pyroligneous acid 251 

Pyrolusite . 123 

Pyrophosphoric acid .... 298 
Pyroxylin 271 

Quantivalence, see Valence. 

Quartz 277 

Quicklime 169 

Quicksilver 182 

Radicals 95, 225, 226 

Radioactivity 176 

Radium 176 

Reactions, Chemical . 28, 37, 136 

Realgar 305 

Red lead 285 

precipitate 184 

prussiate of potash .... 364 

Rennet 272 

Respiration, Animal ... 59, 60 



Retort stands ...... 401 

Retorts 898, 409 

Rhodium .879 

Rochelle salt 257 

Rock-crystal 277 

Rose-quartz 277 

Rose's metal 311 

Rubber stoppers 400 

Rubidium 164 

Ruby 191, 193 

copper 871 

Ruthenium . 379 

Safety matches 294 

Sago 269 

Sal-ammoniac ...... 165 

Saleratus 162 

Soda 163 

Sal-soda 155 

Salt, common 151 

defined 86, 88 

of tartar 162 

Salt-cake . 152 

Saltpeter 163 

Salts classified 88 

nomenclature of ... 21, 91 

Samarium 195 

Sandstone 278 

Saponification 260 

Sapphire 191, 193 

Scandium 147, 190 

Selenite 173 

Selenium 345 

Sesquioxide 74 

Siderite 348 

Siemens- Martin steel process . 357 

Silica : ... 277 

Silicic acid 278 

anhydride 277 

Silicon 277 

Silver 373 

German 181 

Simple radical 95 

Skeletons, Hydrocarbon . . . 219 

Slacked lime 171 

Smithsonite 180 



422 



INDEX. 



Smokeless powder 80 

Soap 259 

bubbles 30, 31 

Soda 155, 156 

Caustic 157 

crystals 155 

saleratus 163 

water 212 

Soda-ash 153 

Sodium 149 

bicarbonate 155 

carbonate 153 

chloride 151 

hydrate 157 

hydroxide 157 

sulphate 152 

Sodium-hydrogen carbonate . 155 

Soft soap 259 

Solar energy 218 

Solder ......... 282 

Soldering 409 

Solution 15 

Solvay process 154 

Soot 203 

Spelter 180 

Sperm-oil 262 

Sphalerite 180 

Stalactites 172,213 

Stalagmites 172, 213 

Stannic acid 283 

Stannous chloride 283 

Starch 121, 269 

Starch-sugar 267 

Stearic acid 254 

Stearine 258 

Steel 319, 355-360 

Chromium 314 

Sterling silver 375 

Stibine 309 

Stibnite 307 

Stoichioinetry 136 

Strass 280 

Strontianite 175 

Strontium 175 

Structural formula 222 

Sucrose 266 



Sugar 265-268 

of lead 252, 286 

of milk 267 

Sulphur ........ 317 

Sulphuret 318 

Sulphureted hydrogen . . . 330 

Sulphur oxides 332-337 

Sulphuric acid 337 

Sulphurous acid 337 

Sulphuryl 332 

Sulphydrates 329 

Superphosphate 291 

Sweet-oil 262 

Symbols, Atomic .... 19, 94 

Graphic 94 

Molecular 20 

Sympathetic ink 368 

Synthesis 24 



196- 



Tallow 

Tantalum .... 
Tapioca .... 
Tartar emetic . . 
Tartaric acid . . . 
Tellurium .... 
Terbium .... 
Test papers . . . 
Test-tubes. . . . 
Tetrad defined . . 
group .... 
Tetrathionic acid . 
Thallium .... 
Thermochemistry . 

Thermometers 

Thionic acids 

Thiosulphuric acid .... 

Thorium 

Thulium 

Tin 

Tinstone 

Tinware 

Titanium 

Toluene 231 

Tongs, Crucible 

Topaz 

Train-oil 



. 38, 



260 
289 
209 
257 
257 
345 
195 
410 
398 
93 
•288 
345 
194 
141 
392 
345 
345 
275 
195 
281 
281 
281 
275 
262 
409 
191 
202 



INDEX. 



423 



Travertine ....... 172 

Triad defined 93 

group 187-195 

Trith ionic acid . . • . . . . 345 

Tufa 172 

Tungsten 316 

Turmeric paper 411 

Turpentine, Oil of 262 

Tuyeres 350 

Type-metal 308 

Typical formula 95 

Uranite 176 

Uranium 316 

Uranyl 316 

Valence 93 

Vanadium 289 

Vaseline 223 

Vegetable life .... 216, 217 
Ventilating chamber .... 410 

Verdigris 252, 372 

Vermillion ....... 184 

Vinegar 252, 253 

Wood ..." 251 

Vitriol, Blue . 372 

Green .... ^ ... 363 

White 182 

Volatile oils .262 

Volumetric combinations, 51, 56, 68, 

71, 74, 75, 111, 134, 139, 297, 

329, 336 

Washing-soda 155 

Water, Composition of , 23, 47, 50, 51 

Contaminated 52 

Hard 174 



Water of crystallization . , . 152 

tests 51 

Water-gas 237 

Water-glass 279 

Wedgewood 403 

Weighing 391 

Welsbach mantles 275 

Whisky 245 

White lead 287 

vitriol 182 

Window-glass 280 

Wine 245 

Wither ite 175 

Wood's metal 311 

Wood-spirit 242 

Wood vinegar 251 

Woulffe bottles 397 

Wrought iron 354 

Xenon 62 

Xylene 231 

Yeast-plant 246 

Yellow chromate of potash . . 315 

prussiate of potash .... 364 

Ytterbium 190 

Yttrium 190 

Zinc 180 

Granulation of .... . 27 

spar 180 

white 181 

Zinc-dust 181 

Zincite 180 

Zirconium 275 



AVERY'S PHYSICS 

By ELROY M. AVERY, Ph.D., LL.D. 



AVERY'S SCHOOL PHYSICS $1.25 

For Secondary Schools 

Avery's School Physics combines in one volume many- 
features which are invaluable in a high school course. Although 
of great comprehensiveness, it is concise and simple. It fur- 
nishes a text which develops in logical order the various divi- 
sions and subdivisions of the science, stating the fundamental 
principles with great accuracy and clearness, and consequently 
affording an excellent basis for the student to use in his work. 
At the same time there are included a large number of exercises 
and experiments which are amply sufficient for class-room demon- 
stration and laboratory practice. 



AVERY'S ELEMENTARY PHYSICS $1.00 

A Short Course for High Schools 

This book meets the wants of schoob that cannot give to 
the study the time required for the author's School Physics, 
and yet demand a book that is scientifically accurate and up- 
to-date in every respect. While following the general lines of 
the larger book, and prepared with the same painstaking 
effort and ability, it contains much matter that is new and 
especially suited for more elementary work. 



AVERY AND CINNOTT'S FIRST LESSONS IN 

PHYSICAL SCIENCE $0.60 

For Grammar Schools 

A work adapted to the capacities of grammar school pupils, 
which wisely selects topics that arc fundamental and immedi- 
ately helpful in other studies, as physical geography and physi- 
ology. The book is of great value to all pupils unable to take 
a high school course in this branch. Although very elementary, 
it is also scientifically accurate. Step by step, the pupil is 
led to a clear understanding of some of the most important 
principles. 



AMERICAN BOOK COMPANY 

[•Ml 



Text-Books in Natural History 



By JAMES G. NEEDHAM, M.S. 
Instructor in Zoology, Knox College, Galesburg, 111. 

NEEDHAM'S ELEMENTARY LESSONS IN ZOOLOGY . 90 cents 

A guide in studying animal life and structure in field and laboratory 
adapted for use in High Schools, Academies, Normal Schools, etc. 
It has been prepared to meet the widely recognized demand for a text- 
book in this department of Natural History which should be brief in 
compass, accurate in statement, and scientific in treatment. 

Some of the leading features of the book are : the selection of 
types for study that are common and easily accessible ; the clear and 
ample directions given for collecting material for study ; the means 
suggested for studying animal life ; the microscopic study of the 
simpler animal types ; the adaptation of the book to the use of schools 
with little material equipment ; the natural and easily comprehensible 
method of classification ; the directions for studying the lives of animals, 
their powers and instincts, morphology, physiology, and natural 
development. 

NEEDHAM'S OUTDOOR STUDIES .... 40 cents 

This little book is intended to supply a series of lessons in Nature 
Study suitable for pupils in the Intermediate or Grammar Grades. 
Designed for pupils of some years of experience and some previous 
training in observation, these lessons are given as guides to close and 
continued observation, and for the educative value of the phenomena of 
nature which they describe. 

As indicated in its title, the book is designed as a guide for field 
work as well as a reader in Nature Study. In connection with the lessons, 
the author gives such simple and explicit directions for field study that 
the pupil may follow them individually without the aid of a teacher. 

Wherever a plant or animal is described, a number is inserted in the 
text referring to a list of scientific names at the end of the book. 



Copies of either of the above books will be sent, prepaid, to any address 
on receipt of the price. 

American Book Company 

New York ♦ Cincinnati ♦ Chicago 

(166) 



Outlines of Botany 

FOR THE 

HIGH SCHOOL LABORATORY AND CLASSROOM 

BY 

ROBERT GREENLEAF LEAVITT, A.M. 
Of the Ames Botanical Laboratory 

Prepared at the request of the Botanical Department cf Harvard 
University 



LEAVITT'S OUTLINES OF BOTANY. Cloth, 8vo. 272 pages . $1.00 
With Gray's Field, Forest, and Garden Flora, 791 pp. . . 1 .80 
With Gray's Manual, 1087 pp 2.25 

This book has been prepared to meet a specific demand. Many 
schools, having outgrown the method of teaching botany hitherto 
prevalent, find the more recent text-books too difficult and comprehensive 
for practical use in an elementary course. In order, therefore, to adapt 
this text-book to present requirements, the author has combined with 
great simplicity and definiteness in presentation, a careful selection and 
a judicious arrangement of matter. It offers 

1. A series of laboratory exercises in the morphology and physiology 

of phanerogams. 

2. Directions for a practical study of typical cryptogams, represent- 

ing the chief groups from the lowest to the highest. 

3. A substantial body of information regarding the forms, activities, 

and relationships of plants, and supplementing the laboratory 
studies. 

The laboratory work is adapted to any equipment, and the instruc- 
tions for it are placed in divisions by themselves, preceding the related 
chapters of descriptive text, which follows in the main the order of 
topics in Gray's Lessons in Botany. Special attention is paid to the 
ecological aspects of plant life, while at the same time morphology and 
physiology are fully treated. 

There are 384 carefully drawn illustrations, many of them entirely 
new. The appendix contains full descriptions of the necessary laboratory 
materials, with directions for their use. It also gives helpful sugges- 
tions for the exercises, addressed primarily to the teacher, and indicating- 
clearly the most effective pedagogical methods. 



Copies sent, prepaid, on receipt of price % 

American Book Company 

New York • Cincinnati • Chicago 

(174) 



A New Astronomy 

BY 

DAVID P. TODD, M.A., Ph.D. 

Professor of Astronomy and Director of the Observatory, Amherst College. 



Cloth, i2mo, 480 pages. Illustrated - - Price, $1.30 



This book is designed for classes pursuing the study in 
High Schools, Academies, and Colleges. The author's 
long experience as a director in astronomical observatories 
and in teaching the subject has given him unusual qualifi- 
cations and advantages for preparing an ideal text-book. 

The noteworthy feature which distinguishes this from 
other text-books on Astronomy is the practical way in 
which the subjects treated are enforced by laboratory 
experiments and methods. In this the author follows the 
principle that Astronomy is preeminently a science of 
observation and should be so taught. 

By placing more importance on the physical than on 
the mathematical facts of Astronomy the author has made 
every page of the book deeply interesting to the student 
and the general reader. The treatment of the planets and 
other heavenly bodies and of the law of universal gravita- 
tion is unusually full, clear, and illuminative. The mar- 
velous discoveries of Astronomy in recent years, and the 
latest advances in methods of teaching the science, are 
all represented. 

The illustrations are an important feature of the book. 
Many of them are so ingeniously devised that they explain 
at a glance what pages of mere description could not make 
clear. 

Copies of Todd's iVero Astronomy will be sent, prepaid, to any address 
on receipt of the price by the Publishers : 

American Book Company 

NEW YORK ♦ CINCINNATI . CHICAGO 

(181) 



A Text-Book of Psychology 

By DANIEL PUTNAM, LL.D. 

Professor of Psychology and Pedagogy in the Michigan State Normal College. 

Cloth, 12mo. 3C0 pa^es. Price, $1.00 



This work is designed especially as a text-book for 
normal schools, high schools, and other secondary schools. 
It is also peculiarly adapted to the needs of Teachers' 
Reading Circles and of private students. The language 
employed is simple, direct, and readily understood by the 
ordinary student. It combines the best of both the new 
and the old in psychology. The existence of an entity 
which may properly be called the mind or soul is recog- 
nized. The vital importance cf mental introspection, as 
the starting point in the study of the mind is emphasized. 
Physiological psychology, without being made unduly 
prominent, is treated with sufficient fulness to show the 
relation of body and mind, an appendix giving helpful 
suggestions for experiments in this line of research. The 
successive steps in the thinking or elaborative process are 
brought out with marked clearness and distinctness. The 
subject of the emotions receives more attention than is 
usually given to this important topic. A chapter is 
devoted to the subject of the moral nature and moral 
law, and the development of a disposition to right con- 
duct. The book presents in the clearest and most concise 
manner, an adequate exposition of the principles of 
psychology. 



Copies of Putnaiiis Psychology will be sent to any address, postpaid, 
on receipt of the price. 

American Book Company 

New York ♦ Cincinnati • Chicago 

(194) 



Scientific Memoir Series 

Edited by JOSEPH S. AMES, Ph.D. 
Johns Hopkins University 



The Free Expansion of Gases. Memoirs by Gay-Lussac, Joule, 
and Joule and Thomson. Edited by Dr. J. S. Ames . 

Prismatic and Diffraction Spectra. Memoirs by Joseph von 
Fraunhofer. Edited by Dr. J. S. Ames 

Rontgen Rays. Memoirs by Rontgen, Stokes, and J. J. Thomson 
Edited by Dr. George F. Barker. .... 

The Modern Theory of Solution. Memoirs by Pfefier.Van't HofT 
Arrhenius, and Raoult. Edited by Dr. II. C. Jones . 

The Laws of Gases. Memoirs by Boyle and Amagat. Edited by 
Dr. Carl Barus .-'.-..„ 

The Second Law of Thermodynamics. Memoirs by Carnot, 
Clausius, and Thomson. Edited by Dr. W. F. Magie 

The Fundamental Laws of Electronic Conduction. Memoirs by 
Faraday, Hittorf, and Kohlrausch. Edited by Dr. H. M 
Goodwin 



The Effects of a Magnetic Field on Radiation. Memoirs by 
Faraday, Kerr, and Zeeman. Edited by Dr. E. P. Lewis 

The Laws of Gravitation. Memoirs by Newton, Bouguer, and 
Cavendish. Edited by Dr. A. S, Mackenzie 

The Wave Theory of Light. Memoirs by Huygens, Young, and 
Fresnel. Edited by Dr. Henry Crew 

The Discovery of Induced Electric Currents. Vol. I. Memoirs 
by Joseph Henry. Edited by Dr. J. S. Ames 

The Discovery of Induced Electric Currents. Vol. II. Memoirs 
by Michael Faraday. Edited by Dr. J. S. Ames . 

Stereochemistry. Memoirs by Pasteur, Le Bel, and Van't HofT, 
together with selections from later memoirs by Wislicenus 
and others. Edited by Dr. G. M. Richardson . 

The Expansion of Gases. Memoirs by Gay-Lussac and Regnault, 
Edited by Prof. W. W. Randall .... 

Radiation and Absorption. Memoirs by Pre'vost, Balfour Stewart, 
Kirchhoff, and Kirchhoff and Bunsen. Edited by Dr, 
DeWitt B. Brace ....... 



$0.75 
.60 
.60 
1.00 
.75 
.90 



.75 

.75 

1 00 

1.00 

.75 

.75 

1.00 
1.00 



LOO 



New York 

(x8 3 ) 



Copies sent, prepaid, to any address on receipt of the price. 

American Book Company 

♦ Cincinnati ♦ Chicago 



A DESCRIPTIVE CATALOGUE OF HIGH 
SCHOOL AND COLLEGE TEXT-BOOKS 

1 A TE issue a complete descriptive catalogue of our 
* ^ text-books for secondary schools and higher 
institutions, illustrated with authors' portraits. 

For the convenience of teachers, separate sections 
are published, devoted to the newest and best books 
in the following branches of study: 

ENGLISH 

MATHEMATICS 

HISTORY AND POLITICAL SCIENCE 

SCIENCE 

MODERN LANGUAGES 

ANCIENT LANGUAGES 

PHILOSOPHY AND EDUCATION 

If you are interested in any of these branches, we 
shall be very glad to send you on request the cata- 
logue sections which you may wish to see. Address 
the nearest office of the Company. 

AMERICAN BOOK COMPANY 

Publishers of School and College Text-Books 
NEW YORK CINCINNATI CHICAGO 

Boston Atlanta Dallas San Francisco 

(312) 



LIBRARY OF CONGRESS 





003 839 141 









